diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 84d992c87888f5a734c57a42a0a62617b465212a..c8a5d932e7677bed9f5b4f87d13e866feb4c7151 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -11538,7 +11538,7 @@ static void CheckForDuplicateEnumValues(Sema &S, Decl **Elements,
   // Populate the EnumMap with all values represented by enum constants without
   // an initialier.
   for (unsigned i = 0; i < NumElements; ++i) {
-    EnumConstantDecl *ECD = cast<EnumConstantDecl>(Elements[i]);
+    EnumConstantDecl *ECD = cast_or_null<EnumConstantDecl>(Elements[i]);
 
     // Null EnumConstantDecl means a previous diagnostic has been emitted for
     // this constant.  Skip this enum since it may be ill-formed.
diff --git a/test/Sema/warn-duplicate-enum.c b/test/Sema/warn-duplicate-enum.c
index 239f6f1995c383043966b4f329d15a56ad6cfc45..f108b3aa6c328da3c463c93d52aa59d76bc60815 100644
--- a/test/Sema/warn-duplicate-enum.c
+++ b/test/Sema/warn-duplicate-enum.c
@@ -90,3 +90,12 @@ enum {
   NMax = N2,
   NCount = NMax + 1
 };
+
+// PR15693
+enum enum1 {
+  VALUE // expected-note{{previous definition is here}}
+};
+
+enum enum2 {
+  VALUE // expected-error{{redefinition of enumerator 'VALUE'}}
+};