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
@@ -913,6 +913,9 @@
   InGroup<IgnoredPragmas>;
 def err_pragma_options_align_mac68k_target_unsupported : Error<
   "mac68k alignment pragma is not supported on this target">;
+def warn_pragma_align_not_xl_compatible : Warning<
+  "#pragma align(packed) may not be compatible with objects generated with AIX XL C/C++">,
+  InGroup<AIXCompat>;
 def warn_pragma_pack_invalid_alignment : Warning<
   "expected #pragma pack parameter to be '1', '2', '4', '8', or '16'">,
   InGroup<IgnoredPragmas>;
diff --git a/clang/lib/Sema/SemaAttr.cpp b/clang/lib/Sema/SemaAttr.cpp
--- a/clang/lib/Sema/SemaAttr.cpp
+++ b/clang/lib/Sema/SemaAttr.cpp
@@ -234,6 +234,8 @@
     // Note that '#pragma options align=packed' is not equivalent to attribute
     // packed, it has a different precedence relative to attribute aligned.
   case POAK_Packed:
+    if (this->Context.getTargetInfo().getTriple().isOSAIX())
+      Diag(PragmaLoc, diag::warn_pragma_align_not_xl_compatible);
     Action = Sema::PSK_Push_Set;
     ModeVal = AlignPackInfo::Packed;
     break;
diff --git a/clang/test/Sema/aix-pragma-align-packed-warn.c b/clang/test/Sema/aix-pragma-align-packed-warn.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/aix-pragma-align-packed-warn.c
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff  -fxl-pragma-pack -verify -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff  -fxl-pragma-pack -verify -fsyntax-only %s
+
+#pragma align(packed) // expected-warning {{#pragma align(packed) may not be compatible with objects generated with AIX XL C/C++}}
+struct A {
+  int a : 8;
+  int   : 0;
+  short s;
+};
+#pragma align(reset)
diff --git a/clang/test/Sema/aix-pragma-pack-and-align.c b/clang/test/Sema/aix-pragma-pack-and-align.c
--- a/clang/test/Sema/aix-pragma-pack-and-align.c
+++ b/clang/test/Sema/aix-pragma-pack-and-align.c
@@ -170,7 +170,7 @@
 } // namespace test7
 
 namespace test8 {
-#pragma align(packed)
+#pragma align(packed) // expected-warning {{#pragma align(packed) may not be compatible with objects generated with AIX XL C/C++}}
 #pragma pack(2)
 #pragma pack(show) // expected-warning {{value of #pragma pack(show) == 2}}
 struct A {