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 +3251,9 @@
     : Warning<"requested alignment must be %0 bytes or smaller; maximum "
               "alignment assumed">,
       InGroup<DiagGroup<"builtin-assume-aligned-alignment">>;
+def warn_not_xl_compatible
+    : Warning<"requesting an alignment of arguments 16 bytes or greater is not"
+              " binary compatible with AIX XL 16.1 and older">;
 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
@@ -3953,6 +3953,13 @@
     return;
 
   uint64_t AlignVal = Alignment.getZExtValue();
+  // 16 byte ByVal alignment not due to a vector member is not honoured by XL
+  // on AIX. Emit a warning here that users are generating binary incompatible
+  // code to be safe.
+  if (const auto *FD = dyn_cast<FieldDecl>(D)) {
+    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
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 +1,17 @@
+// 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}}
+};
+  int a[8] __attribute__((aligned(8)));  // no-warning
+  int b[4] __attribute__((aligned(16))); // no-warning 
+  int c[2] __attribute__((aligned(32))); // no-warning