diff --git a/lib/src/async_environment.dart b/lib/src/async_environment.dart
index 708f3592..bf88b148 100644
--- a/lib/src/async_environment.dart
+++ b/lib/src/async_environment.dart
@@ -717,9 +717,11 @@ class AsyncEnvironment {
     for (var module in _globalModules) {
       var valueInModule = callback(module);
       if (valueInModule != null && value != null) {
-        // TODO(nweiz): List the module URLs.
         throw SassScriptException(
-            'Multiple global modules have a $type named "$name".');
+            'Multiple global modules have a $type named "$name":\n' +
+                bulletedList(_globalModules
+                    .where((module) => callback(module) != null)
+                    .map((module) => p.prettyUri(module.url))));
       }
 
       value = valueInModule;
diff --git a/lib/src/environment.dart b/lib/src/environment.dart
index e728fa0e..059ed0e4 100644
--- a/lib/src/environment.dart
+++ b/lib/src/environment.dart
@@ -5,7 +5,7 @@
 // DO NOT EDIT. This file was generated from async_environment.dart.
 // See tool/grind/synchronize.dart for details.
 //
-// Checksum: fe68ec0b099d3f2992af03dbdaeff0b3e8392808
+// Checksum: 23da0a0dca141c7ac432dc64958c4240eeceb23d
 //
 // ignore_for_file: unused_import
 
@@ -722,9 +722,11 @@ class Environment {
     for (var module in _globalModules) {
       var valueInModule = callback(module);
       if (valueInModule != null && value != null) {
-        // TODO(nweiz): List the module URLs.
         throw SassScriptException(
-            'Multiple global modules have a $type named "$name".');
+            'Multiple global modules have a $type named "$name":\n' +
+                bulletedList(_globalModules
+                    .where((module) => callback(module) != null)
+                    .map((module) => p.prettyUri(module.url))));
       }
 
       value = valueInModule;
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index 5bf5e60a..f48e753a 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -10,6 +10,7 @@ import 'package:charcode/charcode.dart';
 import 'package:collection/collection.dart';
 import 'package:source_span/source_span.dart';
 import 'package:stack_trace/stack_trace.dart';
+import 'package:term_glyph/term_glyph.dart' as glyph;
 
 import 'ast/node.dart';
 import 'util/character.dart';
@@ -38,6 +39,15 @@ String pluralize(String name, int number, {String plural}) {
   return '${name}s';
 }
 
+/// Returns a bulleted list of items in [bullets].
+String bulletedList(Iterable<String> bullets) {
+  return bullets.map((element) {
+    var lines = element.split("\n");
+    return "${glyph.bullet} ${lines.first}" +
+        (lines.length > 1 ? "\n" + indent(lines.skip(1).join("\n"), 2) : "");
+  }).join("\n");
+}
+
 /// Returns the number of times [codeUnit] appears in [string].
 int countOccurrences(String string, int codeUnit) {
   var count = 0;