diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3251,6 +3251,10 @@
     : Warning<"requested alignment must be %0 bytes or smaller; maximum "
               "alignment assumed">,
       InGroup<DiagGroup<"builtin-assume-aligned-alignment">>;
+def warn_not_xl_compatible
+    : Warning<"requested alignment of arguments 16 bytes or greater is not"
+              " compatible with previous versions of the AIX XL compiler">,
+      InGroup<DiagGroup<"builtin-assume-aligned-alignment">>;
 def warn_redeclaration_without_attribute_prev_attribute_ignored : Warning<
   "%q0 redeclared without %1 attribute: previous %1 ignored">,
   InGroup<MicrosoftInconsistentDllImport>;
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -3954,6 +3954,9 @@
 
   uint64_t AlignVal = Alignment.getZExtValue();
 
+  if (Context.getTargetInfo().getTriple().isOSAIX() && (AlignVal >= 16))
+    Diag(AttrLoc, diag::warn_not_xl_compatible) << E->getSourceRange();
+
   // C++11 [dcl.align]p2:
   //   -- if the constant expression evaluates to zero, the alignment
   //      specifier shall have no effect
diff --git a/clang/test/Sema/aix-attr-align.c b/clang/test/Sema/aix-attr-align.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/aix-attr-align.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -verify -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -verify -fsyntax-only %s
+
+struct S {
+  int a[8] __attribute__((aligned(8)));  // no-warning
+};
+
+struct T {
+  int a[4] __attribute__((aligned(16))); // expected-warning {{requested alignment of arguments 16 bytes or greater is not compatible with previous versions of the AIX XL compiler}}
+};
+
+struct U {
+  int a[2] __attribute__((aligned(32))); // expected-warning {{requested alignment of arguments 16 bytes or greater is not compatible with previous versions of the AIX XL compiler}}
+};