diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 974b9b46f6df..6de07e165e6b 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -522,6 +522,9 @@ void X86_64ABIInfo::classify(QualType Ty,
     // FIXME: _Decimal32 and _Decimal64 are SSE.
     // FIXME: _float128 and _Decimal128 are (SSE, SSEUp).
     // FIXME: __int128 is (Integer, Integer).
+  } else if (const EnumType *ET = Ty->getAsEnumType()) {
+    // Classify the underlying integer type.
+    classify(ET->getDecl()->getIntegerType(), Context, OffsetBase, Lo, Hi);
   } else if (Ty->isPointerLikeType() || Ty->isBlockPointerType() ||
              Ty->isObjCQualifiedIdType() ||
              Ty->isObjCQualifiedInterfaceType()) {