diff --git a/src/CodeInspector/ClassMethodChecker.php b/src/CodeInspector/ClassMethodChecker.php
index d2188c1c0..d060685e4 100644
--- a/src/CodeInspector/ClassMethodChecker.php
+++ b/src/CodeInspector/ClassMethodChecker.php
@@ -152,7 +152,8 @@ class ClassMethodChecker extends FunctionChecker
                 }
 
                 foreach ($simple_declared_types as $simple_declared_type) {
-                    if (is_subclass_of($differing_type, $simple_declared_type) ||
+                    if (($simple_declared_type === 'object' && ClassChecker::classExists($differing_type)) ||
+                        ClassChecker::classExtendsOrImplements($differing_type, $simple_declared_type) ||
                         (in_array($differing_type, ['float', 'double', 'int']) && in_array($simple_declared_type, ['float', 'double', 'int'])) ||
                         (in_array($differing_type, ['boolean', 'bool']) && in_array($simple_declared_type, ['boolean', 'bool']))
                     ) {
@@ -715,11 +716,11 @@ class ClassMethodChecker extends FunctionChecker
                     }
                 }
 
-                if (is_subclass_of($method_class, $calling_context) && method_exists($calling_context, $method_name)) {
+                if (ClassChecker::classExtends($method_class, $calling_context) && method_exists($calling_context, $method_name)) {
                     return;
                 }
 
-                if (!is_subclass_of($calling_context, $method_class)) {
+                if (!ClassChecker::classExtends($calling_context, $method_class)) {
                     if (IssueBuffer::accepts(
                         new InaccessibleMethod(
                             'Cannot access protected method ' . $method_id . ' from context ' . $calling_context,
diff --git a/src/CodeInspector/StatementsChecker.php b/src/CodeInspector/StatementsChecker.php
index 5eadce8fc..c1fb1621e 100644
--- a/src/CodeInspector/StatementsChecker.php
+++ b/src/CodeInspector/StatementsChecker.php
@@ -757,7 +757,7 @@ class StatementsChecker
             $use_context = new Context();
 
             if (!$this->_is_static) {
-                $this_class = ClassChecker::getThisClass() && is_subclass_of(ClassChecker::getThisClass(), $this->_absolute_class) ?
+                $this_class = ClassChecker::getThisClass() && ClassChecker::classExtends(ClassChecker::getThisClass(), $this->_absolute_class) ?
                     ClassChecker::getThisClass() :
                     $this->_absolute_class;
 
@@ -1851,7 +1851,7 @@ class StatementsChecker
             if (ClassChecker::getThisClass() &&
                 (
                     ClassChecker::getThisClass() === $this->_absolute_class ||
-                    is_subclass_of(ClassChecker::getThisClass(), $this->_absolute_class) ||
+                    ClassChecker::classExtends(ClassChecker::getThisClass(), $this->_absolute_class) ||
                     trait_exists($this->_absolute_class)
                 )) {
 
@@ -1945,7 +1945,7 @@ class StatementsChecker
                             if (!($this->_source->getSource() instanceof TraitChecker)) {
                                 $calling_context = $this->_absolute_class;
 
-                                if (ClassChecker::getThisClass() && is_subclass_of(ClassChecker::getThisClass(), $this->_absolute_class)) {
+                                if (ClassChecker::getThisClass() && ClassChecker::classExtends(ClassChecker::getThisClass(), $this->_absolute_class)) {
                                     $calling_context = $this->_absolute_class;
                                 }
 
@@ -2752,7 +2752,7 @@ class StatementsChecker
                 }
 
                 if ($input_type_part->value === $param_type_part->value ||
-                    is_subclass_of($input_type_part->value, $param_type_part->value) ||
+                    ClassChecker::classExtends($input_type_part->value, $param_type_part->value) ||
                     self::isMock($input_type_part->value)
                 ) {
                     $type_match_found = true;
@@ -2786,7 +2786,7 @@ class StatementsChecker
                 }
 
 
-                if (is_subclass_of($param_type_part->value, $input_type_part->value)) {
+                if (ClassChecker::classExtends($param_type_part->value, $input_type_part->value)) {
                     // @todo handle coercion
                     $type_match_found = true;
                     break;
diff --git a/src/CodeInspector/Type/Union.php b/src/CodeInspector/Type/Union.php
index 356cd06be..35125cdca 100644
--- a/src/CodeInspector/Type/Union.php
+++ b/src/CodeInspector/Type/Union.php
@@ -3,6 +3,7 @@
 namespace CodeInspector\Type;
 
 use CodeInspector\Type;
+use CodeInspector\ClassChecker;
 
 class Union extends Type
 {
@@ -79,7 +80,7 @@ class Union extends Type
     public function isIn(Union $parent)
     {
         foreach ($this->types as $type) {
-            if (strtoupper($type->value[0]) === $type->value[0] && $parent->hasType('object')) {
+            if ($parent->hasType('object') && ClassChecker::classExists($type->value)) {
                 continue;
             }
 
@@ -88,11 +89,27 @@ class Union extends Type
                 continue;
             }
 
-            if (!$parent->hasType($type->value)) {
-                return false;
+            if ($parent->hasType($type->value)) {
+                continue;
             }
 
-            // @todo add is_subclass_of
+            // last check to see if class is subclass
+            if (ClassChecker::classExists($type->value)) {
+                $type_is_subclass = false;
+
+                foreach ($parent->types as $parent_type) {
+                    if (ClassChecker::classExtendsOrImplements($type->value, $parent_type->value)) {
+                        $type_is_subclass = true;
+                        break;
+                    }
+                }
+
+                if ($type_is_subclass) {
+                    continue;
+                }
+            }
+
+            return false;
         }
 
         return true;