diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 1349b5af6aa55..43e753636d11b 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1515,8 +1515,11 @@ namespace {
       if (FD->getNumParams() == NumBaseParams + 2)
         HasAlignValT = HasSizeT = true;
       else if (FD->getNumParams() == NumBaseParams + 1) {
-        HasSizeT = FD->getParamDecl(NumBaseParams)->getType()->isIntegerType();
-        HasAlignValT = !HasSizeT;
+        QualType ParamTy = FD->getParamDecl(NumBaseParams)->getType();
+        HasAlignValT = ParamTy->isAlignValT();
+        HasSizeT = !HasAlignValT;
+        assert((HasAlignValT || ParamTy->isIntegerType()) &&
+            "Candidate is not regular dealloc function");
       }
 
       // In CUDA, determine how much we'd like / dislike to call this.
diff --git a/clang/test/SemaCXX/cxx03-aligned-allocation-unscoped-enum.cpp b/clang/test/SemaCXX/cxx03-aligned-allocation-unscoped-enum.cpp
new file mode 100644
index 0000000000000..8c8a6bb443797
--- /dev/null
+++ b/clang/test/SemaCXX/cxx03-aligned-allocation-unscoped-enum.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -std=c++03 -triple x86_64-pc-linux-gnu %s \
+// RUN:   -faligned-allocation -emit-llvm -o - | FileCheck %s
+
+// Ensure Clang doesn't confuse std::align_val_t with the sized deallocation
+// parameter when the enum type is unscoped. Libc++ does this in C++03 in order
+// to support aligned allocation in that dialect.
+
+using size_t = __decltype(sizeof(0));
+
+namespace std {
+enum align_val_t { zero = size_t(0),
+                   max = size_t(-1) };
+}
+
+// CHECK-LABEL: define void @_Z1fPi(
+void f(int *p) {
+  // CHECK-NOT: call void @_ZdlPvSt11align_val_t(
+  // CHECK: call void @_ZdlPv(
+  // CHECK: ret void
+  delete p;
+}