diff --git a/lib/src/ast/selector/list.dart b/lib/src/ast/selector/list.dart
index 6904598f..0afff18a 100644
--- a/lib/src/ast/selector/list.dart
+++ b/lib/src/ast/selector/list.dart
@@ -88,12 +88,12 @@ class SelectorList extends Selector {
   ///
   /// The given [parent] may be `null`, indicating that this has no parents. If
   /// so, this list is returned as-is if it doesn't contain any explicit
-  /// [ParentSelector]s. If it does, this throws an [InternalException].
+  /// [ParentSelector]s. If it does, this throws a [SassScriptException].
   SelectorList resolveParentSelectors(SelectorList parent,
       {bool implicitParent: true}) {
     if (parent == null) {
       if (!_containsParentSelector) return this;
-      throw new InternalException(
+      throw new SassScriptException(
           'Top-level selectors may not contain the parent selector "&".');
     }
 
@@ -186,7 +186,7 @@ class SelectorList extends Selector {
     return parent.components.map((complex) {
       var lastComponent = complex.components.last;
       if (lastComponent is! CompoundSelector) {
-        throw new InternalException(
+        throw new SassScriptException(
             'Parent "$complex" is incompatible with this selector.');
       }
 
diff --git a/lib/src/ast/selector/simple.dart b/lib/src/ast/selector/simple.dart
index f108e1d5..25dfb993 100644
--- a/lib/src/ast/selector/simple.dart
+++ b/lib/src/ast/selector/simple.dart
@@ -42,9 +42,9 @@ abstract class SimpleSelector extends Selector {
   /// written with [suffix] at the end.
   ///
   /// Assumes [suffix] is a valid identifier suffix. If this wouldn't produce a
-  /// valid [SimpleSelector], throws an [InternalException].
+  /// valid [SimpleSelector], throws a [SassScriptException].
   SimpleSelector addSuffix(String suffix) =>
-      throw new InternalException('Invalid parent selector "$this"');
+      throw new SassScriptException('Invalid parent selector "$this"');
 
   /// Returns the compoments of a [CompoundSelector] that matches only elements
   /// matched by both this and [compound].
diff --git a/lib/src/exception.dart b/lib/src/exception.dart
index 938fac73..914ed83f 100644
--- a/lib/src/exception.dart
+++ b/lib/src/exception.dart
@@ -41,16 +41,16 @@ class SassFormatException extends SourceSpanFormatException
   SassFormatException(String message, FileSpan span) : super(message, span);
 }
 
-/// An exception thrown by SassScript that doesn't yet have a [FileSpan]
-/// associated with it.
+/// An exception thrown by SassScript.
 ///
-/// This is caught by Sass and converted to a [SassRuntimeException] with a
-/// source span and a stack trace.
-class InternalException {
+/// This doesn't extends [SassException] because it doesn't (yet) have a
+/// [FileSpan] associated with it. It's caught by Sass's internals and converted
+/// to a [SassRuntimeException] with a source span and a stack trace.
+class SassScriptException {
   /// The error message.
   final String message;
 
-  InternalException(this.message);
+  SassScriptException(this.message);
 
   String toString() => "$message\n\nBUG: This should include a source span!";
 }
diff --git a/lib/src/functions.dart b/lib/src/functions.dart
index 09648455..3e6179ce 100644
--- a/lib/src/functions.dart
+++ b/lib/src/functions.dart
@@ -263,7 +263,7 @@ void defineCoreFunctions(Environment environment) {
       }
 
       assert(arguments.length != 1);
-      throw new InternalException(
+      throw new SassScriptException(
           "Only 1 argument allowed, but ${arguments.length} were passed.");
     }
   ]));
@@ -289,7 +289,7 @@ void defineCoreFunctions(Environment environment) {
     var color = arguments[0].assertColor("color");
     var argumentList = arguments[1] as SassArgumentList;
     if (argumentList.contents.isNotEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "Only only positional argument is allowed. All other arguments must "
           "be passed by name.");
     }
@@ -307,7 +307,7 @@ void defineCoreFunctions(Environment environment) {
     var alpha = getInRange("alpha", -1, 1);
 
     if (keywords.isNotEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "No ${pluralize('argument', keywords.length)} named "
           "${toSentence(keywords.keys.map((name) => "\$$name"), 'or')}.");
     }
@@ -316,7 +316,7 @@ void defineCoreFunctions(Environment environment) {
     var hasHsl = hue != null || saturation != null || lightness != null;
     if (hasRgb) {
       if (hasHsl) {
-        throw new InternalException(
+        throw new SassScriptException(
             "RGB parameters may not be passed along with HSL parameters.");
       }
 
@@ -340,7 +340,7 @@ void defineCoreFunctions(Environment environment) {
     var color = arguments[0].assertColor("color");
     var argumentList = arguments[1] as SassArgumentList;
     if (argumentList.contents.isNotEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "Only only positional argument is allowed. All other arguments must "
           "be passed by name.");
     }
@@ -367,7 +367,7 @@ void defineCoreFunctions(Environment environment) {
     var alpha = getScale("alpha");
 
     if (keywords.isNotEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "No ${pluralize('argument', keywords.length)} named "
           "${toSentence(keywords.keys.map((name) => "\$$name"), 'or')}.");
     }
@@ -376,7 +376,7 @@ void defineCoreFunctions(Environment environment) {
     var hasHsl = saturation != null || lightness != null;
     if (hasRgb) {
       if (hasHsl) {
-        throw new InternalException(
+        throw new SassScriptException(
             "RGB parameters may not be passed along with HSL parameters.");
       }
 
@@ -400,7 +400,7 @@ void defineCoreFunctions(Environment environment) {
     var color = arguments[0].assertColor("color");
     var argumentList = arguments[1] as SassArgumentList;
     if (argumentList.contents.isNotEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "Only only positional argument is allowed. All other arguments must "
           "be passed by name.");
     }
@@ -418,7 +418,7 @@ void defineCoreFunctions(Environment environment) {
     var alpha = getInRange("alpha", 0, 1);
 
     if (keywords.isNotEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "No ${pluralize('argument', keywords.length)} named "
           "${toSentence(keywords.keys.map((name) => "\$$name"), 'or')}.");
     }
@@ -427,7 +427,7 @@ void defineCoreFunctions(Environment environment) {
     var hasHsl = saturation != null || lightness != null;
     if (hasRgb) {
       if (hasHsl) {
-        throw new InternalException(
+        throw new SassScriptException(
             "RGB parameters may not be passed along with HSL parameters.");
       }
 
@@ -542,7 +542,7 @@ void defineCoreFunctions(Environment environment) {
       if (max == null || max.lessThan(number).isTruthy) max = number;
     }
     if (max != null) return max;
-    throw new InternalException("At least one argument must be passed.");
+    throw new SassScriptException("At least one argument must be passed.");
   });
 
   environment.defineFunction("min", r"$numbers...", (arguments) {
@@ -552,14 +552,14 @@ void defineCoreFunctions(Environment environment) {
       if (min == null || min.greaterThan(number).isTruthy) min = number;
     }
     if (min != null) return min;
-    throw new InternalException("At least one argument must be passed.");
+    throw new SassScriptException("At least one argument must be passed.");
   });
 
   environment.defineFunction("random", r"$limit: null", (arguments) {
     if (arguments[0] == sassNull) return new SassNumber(_random.nextDouble());
     var limit = arguments[0].assertNumber("limit").assertInt("limit");
     if (limit < 1) {
-      throw new InternalException(
+      throw new SassScriptException(
           "\$limit: Must be greater than 0, was $limit.");
     }
     return new SassNumber(_random.nextInt(limit + 1) + 1);
@@ -607,7 +607,7 @@ void defineCoreFunctions(Environment environment) {
     } else if (separatorParam.text == "comma") {
       separator = ListSeparator.comma;
     } else {
-      throw new InternalException(
+      throw new SassScriptException(
           '\$$separator: Must be "space", "comma", or "auto".');
     }
 
@@ -636,7 +636,7 @@ void defineCoreFunctions(Environment environment) {
     } else if (separatorParam.text == "comma") {
       separator = ListSeparator.comma;
     } else {
-      throw new InternalException(
+      throw new SassScriptException(
           '\$$separator: Must be "space", "comma", or "auto".');
     }
 
@@ -725,7 +725,7 @@ void defineCoreFunctions(Environment environment) {
       return new SassMap(
           mapMap(argumentList.keywords, key: (key, _) => new SassString(key)));
     } else {
-      throw new InternalException(
+      throw new SassScriptException(
           "\$args: $argumentList is not an argument list.");
     }
   });
@@ -735,7 +735,7 @@ void defineCoreFunctions(Environment environment) {
   environment.defineFunction("selector-nest", r"$selectors...", (arguments) {
     var selectors = (arguments[0] as SassArgumentList).contents;
     if (selectors.isEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "\$selectors: At least one selector must be passed.");
     }
 
@@ -748,7 +748,7 @@ void defineCoreFunctions(Environment environment) {
   environment.defineFunction("selector-append", r"$selectors...", (arguments) {
     var selectors = (arguments[0] as SassArgumentList).contents;
     if (selectors.isEmpty) {
-      throw new InternalException(
+      throw new SassScriptException(
           "\$selectors: At least one selector must be passed.");
     }
 
@@ -760,13 +760,13 @@ void defineCoreFunctions(Environment environment) {
         if (compound is CompoundSelector) {
           var newCompound = _prependParent(compound);
           if (newCompound == null) {
-            throw new InternalException("Can't append $complex to $parent.");
+            throw new SassScriptException("Can't append $complex to $parent.");
           }
 
           return new ComplexSelector(
               [newCompound]..addAll(complex.components.skip(1)));
         } else {
-          throw new InternalException("Can't append $complex to $parent.");
+          throw new SassScriptException("Can't append $complex to $parent.");
         }
       })).resolveParentSelectors(parent);
     }).asSassList;
@@ -899,7 +899,7 @@ void defineCoreFunctions(Environment environment) {
 ///
 /// If [number] has no units, its value is clamped to be greater than `0` or
 /// less than [max] and returned. If [number] is a percentage, it's scaled to be
-/// within `0` and [max]. Otherwise, this throws an [InternalException].
+/// within `0` and [max]. Otherwise, this throws a [SassScriptException].
 ///
 /// [name] is used to identify the argument in the error message.
 num _percentageOrUnitless(SassNumber number, num max, String name) {
@@ -909,7 +909,7 @@ num _percentageOrUnitless(SassNumber number, num max, String name) {
   } else if (number.hasUnit("%")) {
     value = max * number.value / 100;
   } else {
-    throw new InternalException(
+    throw new SassScriptException(
         '\$$name: Expected $number to have no units or "%".');
   }
 
diff --git a/lib/src/value.dart b/lib/src/value.dart
index 817bb5c3..9e3977d3 100644
--- a/lib/src/value.dart
+++ b/lib/src/value.dart
@@ -62,7 +62,7 @@ abstract class Value {
   /// Calls the appropriate visit method on [visitor].
   /*=T*/ accept/*<T>*/(ValueVisitor/*<T>*/ visitor);
 
-  /// Throws an [InternalException] if [this] isn't a boolean.
+  /// Throws a [SassScriptException] if [this] isn't a boolean.
   ///
   /// Note that generally, functions should use [isTruthy] rather than requiring
   /// a literal boolean.
@@ -72,28 +72,28 @@ abstract class Value {
   SassBoolean assertBoolean([String name]) =>
       throw _exception("$this is not a boolean.", name);
 
-  /// Throws an [InternalException] if [this] isn't a color.
+  /// Throws a [SassScriptException] if [this] isn't a color.
   ///
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`). It's used for debugging.
   SassColor assertColor([String name]) =>
       throw _exception("$this is not a color.", name);
 
-  /// Throws an [InternalException] if [this] isn't a map.
+  /// Throws a [SassScriptException] if [this] isn't a map.
   ///
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`). It's used for debugging.
   SassMap assertMap([String name]) =>
       throw _exception("$this is not a map.", name);
 
-  /// Throws an [InternalException] if [this] isn't a number.
+  /// Throws a [SassScriptException] if [this] isn't a number.
   ///
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`). It's used for debugging.
   SassNumber assertNumber([String name]) =>
       throw _exception("$this is not a number.", name);
 
-  /// Throws an [InternalException] if [this] isn't a string.
+  /// Throws a [SassScriptException] if [this] isn't a string.
   ///
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`). It's used for debugging.
@@ -103,7 +103,7 @@ abstract class Value {
   /// Parses [this] as a selector list, in the same manner as the
   /// `selector-parse()` function.
   ///
-  /// Throws an [InternalException] if this isn't a type that can be parsed as a
+  /// Throws a [SassScriptException] if this isn't a type that can be parsed as a
   /// selector, or if parsing fails. If [allowParent] is `true`, this allows
   /// [ParentSelector]s. Otherwise, they're considered parse errors.
   ///
@@ -123,7 +123,7 @@ abstract class Value {
   /// Parses [this] as a simple selector, in the same manner as the
   /// `selector-parse()` function.
   ///
-  /// Throws an [InternalException] if this isn't a type that can be parsed as a
+  /// Throws a [SassScriptException] if this isn't a type that can be parsed as a
   /// selector, or if parsing fails. If [allowParent] is `true`, this allows
   /// [ParentSelector]s. Otherwise, they're considered parse errors.
   ///
@@ -143,7 +143,7 @@ abstract class Value {
   /// Parses [this] as a compound selector, in the same manner as the
   /// `selector-parse()` function.
   ///
-  /// Throws an [InternalException] if this isn't a type that can be parsed as a
+  /// Throws a [SassScriptException] if this isn't a type that can be parsed as a
   /// selector, or if parsing fails. If [allowParent] is `true`, this allows
   /// [ParentSelector]s. Otherwise, they're considered parse errors.
   ///
@@ -164,7 +164,7 @@ abstract class Value {
   /// Converts a `selector-parse()`-style input into a string that can be
   /// parsed.
   ///
-  /// Throws an [InternalException] if [this] isn't a type or a structure that
+  /// Throws a [SassScriptException] if [this] isn't a type or a structure that
   /// can be parsed as a selector.
   String _selectorString([String name]) {
     var string = _selectorStringOrNull();
@@ -229,27 +229,27 @@ abstract class Value {
 
   /// The SassScript `>` operation.
   SassBoolean greaterThan(Value other) =>
-      throw new InternalException('Undefined operation "$this > $other".');
+      throw new SassScriptException('Undefined operation "$this > $other".');
 
   /// The SassScript `>=` operation.
   SassBoolean greaterThanOrEquals(Value other) =>
-      throw new InternalException('Undefined operation "$this >= $other".');
+      throw new SassScriptException('Undefined operation "$this >= $other".');
 
   /// The SassScript `<` operation.
   SassBoolean lessThan(Value other) =>
-      throw new InternalException('Undefined operation "$this < $other".');
+      throw new SassScriptException('Undefined operation "$this < $other".');
 
   /// The SassScript `<=` operation.
   SassBoolean lessThanOrEquals(Value other) =>
-      throw new InternalException('Undefined operation "$this <= $other".');
+      throw new SassScriptException('Undefined operation "$this <= $other".');
 
   /// The SassScript `*` operation.
   Value times(Value other) =>
-      throw new InternalException('Undefined operation "$this * $other".');
+      throw new SassScriptException('Undefined operation "$this * $other".');
 
   /// The SassScript `%` operation.
   Value modulo(Value other) =>
-      throw new InternalException('Undefined operation "$this % $other".');
+      throw new SassScriptException('Undefined operation "$this % $other".');
 
   /// The SassScript `+` operation.
   Value plus(Value other) {
@@ -288,7 +288,7 @@ abstract class Value {
   /// instead to convert [this] to CSS.
   String toString() => valueToCss(this, inspect: true);
 
-  /// Throws an [InternalException] with the given [message].
-  InternalException _exception(String message, [String name]) =>
-      new InternalException(name == null ? message : "\$$name: $message");
+  /// Throws a [SassScriptException] with the given [message].
+  SassScriptException _exception(String message, [String name]) =>
+      new SassScriptException(name == null ? message : "\$$name: $message");
 }
diff --git a/lib/src/value/color.dart b/lib/src/value/color.dart
index 15d512dd..5a9d6ccd 100644
--- a/lib/src/value/color.dart
+++ b/lib/src/value/color.dart
@@ -107,23 +107,23 @@ class SassColor extends Value {
 
   Value plus(Value other) {
     if (other is! SassNumber && other is! SassColor) return super.plus(other);
-    throw new InternalException('Undefined operation "$this + $other".');
+    throw new SassScriptException('Undefined operation "$this + $other".');
   }
 
   Value minus(Value other) {
     if (other is! SassNumber && other is! SassColor) return super.minus(other);
-    throw new InternalException('Undefined operation "$this - $other".');
+    throw new SassScriptException('Undefined operation "$this - $other".');
   }
 
   Value dividedBy(Value other) {
     if (other is! SassNumber && other is! SassColor) {
       return super.dividedBy(other);
     }
-    throw new InternalException('Undefined operation "$this / $other".');
+    throw new SassScriptException('Undefined operation "$this / $other".');
   }
 
   Value modulo(Value other) =>
-      throw new InternalException('Undefined operation "$this % $other".');
+      throw new SassScriptException('Undefined operation "$this % $other".');
 
   bool operator ==(other) =>
       other is SassColor &&
diff --git a/lib/src/value/number.dart b/lib/src/value/number.dart
index d556f550..94f966f6 100644
--- a/lib/src/value/number.dart
+++ b/lib/src/value/number.dart
@@ -206,7 +206,7 @@ class SassNumber extends Value {
   /// Returns [value] as an [int], if it's an integer value according to
   /// [isInt].
   ///
-  /// Throws an [InternalException] if [value] isn't an integer. If this came
+  /// Throws a [SassScriptException] if [value] isn't an integer. If this came
   /// from a function argument, [name] is the argument name (without the `$`).
   /// It's used for debugging.
   int assertInt([String name]) {
@@ -221,7 +221,7 @@ class SassNumber extends Value {
   /// A Sass-style index is one-based, and uses negative numbers to count
   /// backwards from the end of the list.
   ///
-  /// Throws an [InternalException] if this isn't an integer or if it isn't a
+  /// Throws a [SassScriptException] if this isn't an integer or if it isn't a
   /// valid index for [list]. If this came from a function argument, [name] is
   /// the argument name (without the `$`). It's used for debugging.
   int assertIndexFor(List list, [String name]) {
@@ -238,7 +238,7 @@ class SassNumber extends Value {
   /// If [value] is between [min] and [max], returns it.
   ///
   /// If [value] is [fuzzyEquals] to [min] or [max], it's clamped to the
-  /// appropriate value. Otherwise, this throws an [InternalException]. If this
+  /// appropriate value. Otherwise, this throws a [SassScriptException]. If this
   /// came from a function argument, [name] is the argument name (without the
   /// `$`). It's used for debugging.
   num valueInRange(num min, num max, [String name]) {
@@ -254,7 +254,7 @@ class SassNumber extends Value {
       denominatorUnits.isEmpty &&
       numeratorUnits.first == unit;
 
-  /// Throws an [InternalException] unless [this] has [unit] as its only unit
+  /// Throws a [SassScriptException] unless [this] has [unit] as its only unit
   /// (and as a numerator).
   ///
   /// If this came from a function argument, [name] is the argument name
@@ -264,7 +264,7 @@ class SassNumber extends Value {
     throw _exception('Expected $this to have unit "$unit".');
   }
 
-  /// Throws an [InternalException] unless [this] has no units.
+  /// Throws a [SassScriptException] unless [this] has no units.
   ///
   /// If this came from a function argument, [name] is the argument name
   /// (without the `$`). It's used for debugging.
@@ -276,7 +276,7 @@ class SassNumber extends Value {
   /// Returns [value], converted to the units represented by [newNumerators] and
   /// [newDenominators].
   ///
-  /// Throws an [InternalException] if this number's units aren't compatible
+  /// Throws a [SassScriptException] if this number's units aren't compatible
   /// with [newNumerators] and [newDenominators].
   num valueInUnits(List<String> newNumerators, List<String> newDenominators) {
     if ((newNumerators.isEmpty && newDenominators.isEmpty) ||
@@ -295,7 +295,7 @@ class SassNumber extends Value {
         value *= factor;
         return true;
       }, orElse: () {
-        throw new InternalException("Incompatible units "
+        throw new SassScriptException("Incompatible units "
             "${_unitString(this.numeratorUnits, this.denominatorUnits)} and "
             "${_unitString(newNumerators, newDenominators)}.");
       });
@@ -309,14 +309,14 @@ class SassNumber extends Value {
         value *= factor;
         return true;
       }, orElse: () {
-        throw new InternalException("Incompatible units "
+        throw new SassScriptException("Incompatible units "
             "${_unitString(this.numeratorUnits, this.denominatorUnits)} and "
             "${_unitString(newNumerators, newDenominators)}.");
       });
     }
 
     if (oldNumerators.isNotEmpty || oldDenominators.isNotEmpty) {
-      throw new InternalException("Incompatible units "
+      throw new SassScriptException("Incompatible units "
           "${_unitString(this.numeratorUnits, this.denominatorUnits)} and "
           "${_unitString(newNumerators, newDenominators)}.");
     }
@@ -333,7 +333,7 @@ class SassNumber extends Value {
     try {
       greaterThan(other);
       return true;
-    } on InternalException {
+    } on SassScriptException {
       return false;
     }
   }
@@ -343,7 +343,7 @@ class SassNumber extends Value {
       return new SassBoolean(
           _coerceUnits(other, (num1, num2) => fuzzyGreaterThan(num1, num2)));
     }
-    throw new InternalException('Undefined operation "$this > $other".');
+    throw new SassScriptException('Undefined operation "$this > $other".');
   }
 
   SassBoolean greaterThanOrEquals(Value other) {
@@ -351,7 +351,7 @@ class SassNumber extends Value {
       return new SassBoolean(_coerceUnits(
           other, (num1, num2) => fuzzyGreaterThanOrEquals(num1, num2)));
     }
-    throw new InternalException('Undefined operation "$this >= $other".');
+    throw new SassScriptException('Undefined operation "$this >= $other".');
   }
 
   SassBoolean lessThan(Value other) {
@@ -359,7 +359,7 @@ class SassNumber extends Value {
       return new SassBoolean(
           _coerceUnits(other, (num1, num2) => fuzzyLessThan(num1, num2)));
     }
-    throw new InternalException('Undefined operation "$this < $other".');
+    throw new SassScriptException('Undefined operation "$this < $other".');
   }
 
   SassBoolean lessThanOrEquals(Value other) {
@@ -367,14 +367,14 @@ class SassNumber extends Value {
       return new SassBoolean(_coerceUnits(
           other, (num1, num2) => fuzzyLessThanOrEquals(num1, num2)));
     }
-    throw new InternalException('Undefined operation "$this <= $other".');
+    throw new SassScriptException('Undefined operation "$this <= $other".');
   }
 
   Value modulo(Value other) {
     if (other is SassNumber) {
       return new SassNumber(_coerceUnits(other, (num1, num2) => num1 % num2));
     }
-    throw new InternalException('Undefined operation "$this % $other".');
+    throw new SassScriptException('Undefined operation "$this % $other".');
   }
 
   Value plus(Value other) {
@@ -382,7 +382,7 @@ class SassNumber extends Value {
       return new SassNumber(_coerceUnits(other, (num1, num2) => num1 + num2));
     }
     if (other is! SassColor) return super.plus(other);
-    throw new InternalException('Undefined operation "$this + $other".');
+    throw new SassScriptException('Undefined operation "$this + $other".');
   }
 
   Value minus(Value other) {
@@ -390,7 +390,7 @@ class SassNumber extends Value {
       return new SassNumber(_coerceUnits(other, (num1, num2) => num1 - num2));
     }
     if (other is! SassColor) return super.minus(other);
-    throw new InternalException('Undefined operation "$this - $other".');
+    throw new SassScriptException('Undefined operation "$this - $other".');
   }
 
   Value times(Value other) {
@@ -398,7 +398,7 @@ class SassNumber extends Value {
       return _multiplyUnits(this.value * other.value, this.numeratorUnits,
           this.denominatorUnits, other.numeratorUnits, other.denominatorUnits);
     }
-    throw new InternalException('Undefined operation "$this * $other".');
+    throw new SassScriptException('Undefined operation "$this * $other".');
   }
 
   Value dividedBy(Value other) {
@@ -407,7 +407,7 @@ class SassNumber extends Value {
           this.denominatorUnits, other.denominatorUnits, other.numeratorUnits);
     }
     if (other is! SassColor) super.dividedBy(other);
-    throw new InternalException('Undefined operation "$this / $other".');
+    throw new SassScriptException('Undefined operation "$this / $other".');
   }
 
   Value unaryPlus() => this;
@@ -417,7 +417,7 @@ class SassNumber extends Value {
   /// Converts [other]'s value to be compatible with this number's, and calls
   /// [operation] with the resulting numbers.
   ///
-  /// Throws an [InternalException] if the two numbers' units are incompatible.
+  /// Throws a [SassScriptException] if the two numbers' units are incompatible.
   /*=T*/ _coerceUnits/*<T>*/(
       SassNumber other, /*=T*/ operation(num num1, num num2)) {
     num num1;
@@ -530,7 +530,7 @@ class SassNumber extends Value {
 
   int get hashCode => fuzzyHashCode(value);
 
-  /// Throws an [InternalException] with the given [message].
-  InternalException _exception(String message, [String name]) =>
-      new InternalException(name == null ? message : "\$$name: $message");
+  /// Throws a [SassScriptException] with the given [message].
+  SassScriptException _exception(String message, [String name]) =>
+      new SassScriptException(name == null ? message : "\$$name: $message");
 }
diff --git a/lib/src/visitor/perform.dart b/lib/src/visitor/perform.dart
index d84d49a1..4e6e52a4 100644
--- a/lib/src/visitor/perform.dart
+++ b/lib/src/visitor/perform.dart
@@ -1229,12 +1229,12 @@ class _PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
     }
   }
 
-  /// Runs [callback], and converts any [InternalException]s it throws to
+  /// Runs [callback], and converts any [SassScriptException]s it throws to
   /// [SassRuntimeException]s with [span].
   /*=T*/ _addExceptionSpan/*<T>*/(FileSpan span, /*=T*/ callback()) {
     try {
       return callback();
-    } on InternalException catch (error) {
+    } on SassScriptException catch (error) {
       throw _exception(error.message, span);
     }
   }
diff --git a/lib/src/visitor/serialize.dart b/lib/src/visitor/serialize.dart
index 66296ac8..b197ec46 100644
--- a/lib/src/visitor/serialize.dart
+++ b/lib/src/visitor/serialize.dart
@@ -45,7 +45,7 @@ String toCss(CssNode node, {OutputStyle style, bool inspect: false}) {
 /// If [inspect] is `true`, this will emit an unambiguous representation of the
 /// source structure. Note however that, although this will be valid SCSS, it
 /// may not be valid CSS. If [inspect] is `false` and [value] can't be
-/// represented in plain CSS, throws an [InternalException].
+/// represented in plain CSS, throws a [SassScriptException].
 String valueToCss(Value value, {bool inspect: false}) {
   var visitor = new _SerializeCssVisitor(inspect: inspect);
   value.accept(visitor);
@@ -57,7 +57,7 @@ String valueToCss(Value value, {bool inspect: false}) {
 /// If [inspect] is `true`, this will emit an unambiguous representation of the
 /// source structure. Note however that, although this will be valid SCSS, it
 /// may not be valid CSS. If [inspect] is `false` and [selector] can't be
-/// represented in plain CSS, throws an [InternalException].
+/// represented in plain CSS, throws a [SassScriptException].
 String selectorToCss(Selector selector, {bool inspect: false}) {
   var visitor = new _SerializeCssVisitor(inspect: inspect);
   selector.accept(visitor);
@@ -247,11 +247,11 @@ class _SerializeCssVisitor
   // ## Values
 
   /// Converts [value] to a plain CSS string, converting any
-  /// [InternalException]s to [SassException]s.
+  /// [SassScriptException]s to [SassException]s.
   void _visitValue(CssValue<Value> value) {
     try {
       value.value.accept(this);
-    } on InternalException catch (error) {
+    } on SassScriptException catch (error) {
       throw new SassException(error.message, value.span);
     }
   }
@@ -283,7 +283,9 @@ class _SerializeCssVisitor
     if (value.hasBrackets) {
       _buffer.writeCharCode($lbracket);
     } else if (value.contents.isEmpty) {
-      if (!_inspect) throw new InternalException("() isn't a valid CSS value");
+      if (!_inspect) {
+        throw new SassScriptException("() isn't a valid CSS value");
+      }
       _buffer.write("()");
       return;
     }
@@ -317,7 +319,9 @@ class _SerializeCssVisitor
   }
 
   void visitMap(SassMap map) {
-    if (!_inspect) throw new InternalException("$map isn't a valid CSS value.");
+    if (!_inspect) {
+      throw new SassScriptException("$map isn't a valid CSS value.");
+    }
     _buffer.writeCharCode($lparen);
     _writeBetween(map.contents.keys, ", ", (key) {
       _writeMapElement(key);
@@ -347,7 +351,7 @@ class _SerializeCssVisitor
     if (!_inspect) {
       if (value.numeratorUnits.length > 1 ||
           value.denominatorUnits.isNotEmpty) {
-        throw new InternalException("$value isn't a valid CSS value.");
+        throw new SassScriptException("$value isn't a valid CSS value.");
       }
 
       if (value.numeratorUnits.isNotEmpty) {