diff --git a/llvm/lib/Support/SmallVector.cpp b/llvm/lib/Support/SmallVector.cpp
--- a/llvm/lib/Support/SmallVector.cpp
+++ b/llvm/lib/Support/SmallVector.cpp
@@ -19,12 +19,21 @@
 
 // Check that no bytes are wasted and everything is well-aligned.
 namespace {
+#if defined(_AIX) && __open_xl_version__ >= 17
+struct Struct16B {
+  void *X __align(16);
+};
+struct Struct32B {
+  void *X __align(32);
+};
+#else
 struct Struct16B {
   alignas(16) void *X;
 };
 struct Struct32B {
   alignas(32) void *X;
 };
+#endif
 }
 static_assert(sizeof(SmallVector<void *, 0>) ==
                   sizeof(unsigned) * 2 + sizeof(void *),