Index: lib/AST/ASTStructuralEquivalence.cpp
===================================================================
--- lib/AST/ASTStructuralEquivalence.cpp
+++ lib/AST/ASTStructuralEquivalence.cpp
@@ -1178,6 +1178,14 @@
 /// Determine structural equivalence of two enums.
 static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                      EnumDecl *D1, EnumDecl *D2) {
+
+  // Compare the definitions of these two eunums. If either or both are
+  // incomplete (i.e. forward declared), we assume that they are equivalent.
+  D1 = D1->getDefinition();
+  D2 = D2->getDefinition();
+  if (!D1 || !D2)
+    return true;
+
   EnumDecl::enumerator_iterator EC2 = D2->enumerator_begin(),
                                 EC2End = D2->enumerator_end();
   for (EnumDecl::enumerator_iterator EC1 = D1->enumerator_begin(),
Index: unittests/AST/StructuralEquivalenceTest.cpp
===================================================================
--- unittests/AST/StructuralEquivalenceTest.cpp
+++ unittests/AST/StructuralEquivalenceTest.cpp
@@ -618,6 +618,31 @@
   EXPECT_FALSE(testStructuralMatch(R0, R1));
 }
 
+TEST_F(StructuralEquivalenceRecordTest,
+    FwdDeclRecordShouldBeEqualWithFwdDeclRecord) {
+  auto t = makeNamedDecls("class foo;", "class foo;", Lang_CXX11);
+  EXPECT_TRUE(testStructuralMatch(t));
+}
+
+TEST_F(StructuralEquivalenceRecordTest,
+       FwdDeclRecordShouldBeEqualWithRecordWhichHasDefinition) {
+  auto t =
+      makeNamedDecls("class foo;", "class foo { int A; };", Lang_CXX11);
+  EXPECT_TRUE(testStructuralMatch(t));
+}
+
+TEST_F(StructuralEquivalenceRecordTest,
+       RecordShouldBeEqualWithRecordWhichHasDefinition) {
+  auto t = makeNamedDecls("class foo { int A; };", "class foo { int A; };",
+                          Lang_CXX11);
+  EXPECT_TRUE(testStructuralMatch(t));
+}
+
+TEST_F(StructuralEquivalenceRecordTest, RecordsWithDifferentBody) {
+  auto t = makeNamedDecls("class foo { int B; };", "class foo { int A; };",
+                          Lang_CXX11);
+  EXPECT_FALSE(testStructuralMatch(t));
+}
 
 TEST_F(StructuralEquivalenceTest, CompareSameDeclWithMultiple) {
   auto t = makeNamedDecls(
@@ -627,5 +652,33 @@
   EXPECT_FALSE(testStructuralMatch(t));
 }
 
+struct StructuralEquivalenceEnumTest : StructuralEquivalenceTest {};
+
+TEST_F(StructuralEquivalenceEnumTest, FwdDeclEnumShouldBeEqualWithFwdDeclEnum) {
+  auto t = makeNamedDecls("enum class foo;", "enum class foo;", Lang_CXX11);
+  EXPECT_TRUE(testStructuralMatch(t));
+}
+
+TEST_F(StructuralEquivalenceEnumTest,
+       FwdDeclEnumShouldBeEqualWithEnumWhichHasDefinition) {
+  auto t =
+      makeNamedDecls("enum class foo;", "enum class foo { A };", Lang_CXX11);
+  EXPECT_TRUE(testStructuralMatch(t));
+}
+
+TEST_F(StructuralEquivalenceEnumTest,
+       EnumShouldBeEqualWithEnumWhichHasDefinition) {
+  auto t = makeNamedDecls("enum class foo { A };", "enum class foo { A };",
+                          Lang_CXX11);
+  EXPECT_TRUE(testStructuralMatch(t));
+}
+
+TEST_F(StructuralEquivalenceEnumTest, EnumsWithDifferentBody) {
+  auto t = makeNamedDecls("enum class foo { B };", "enum class foo { A };",
+                          Lang_CXX11);
+  EXPECT_FALSE(testStructuralMatch(t));
+}
+
+
 } // end namespace ast_matchers
 } // end namespace clang