diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -1083,6 +1083,9 @@
 // A warning group for warnings about code that clang accepts but gcc doesn't.
 def GccCompat : DiagGroup<"gcc-compat">;
 
+// A warning group for warnings about code that may be incompatible on AIX.
+def AIXCompat : DiagGroup<"aix-compat">;
+
 // Warnings for Microsoft extensions.
 def MicrosoftCharize : DiagGroup<"microsoft-charize">;
 def MicrosoftDrectveSection : DiagGroup<"microsoft-drectve-section">;
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
@@ -3254,6 +3254,10 @@
     : Warning<"requested alignment must be %0 bytes or smaller; maximum "
               "alignment assumed">,
       InGroup<DiagGroup<"builtin-assume-aligned-alignment">>;
+def warn_not_xl_compatible
+    : Warning<"requesting an alignment of 16 bytes or greater for struct"
+              " members is not binary compatible with AIX XL 16.1 and older">,
+      InGroup<AIXCompat>;
 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 +3953,12 @@
     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 (AlignVal >= 16 && isa<FieldDecl>(D) &&
+      Context.getTargetInfo().getTriple().isOSAIX())
+    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 +1,22 @@
+// off-no-diagnostics
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -verify -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -verify -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -verify=off -Wno-aix-compat -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -verify=off -Wno-aix-compat -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc64le-unknown-linux -verify=off -fsyntax-only %s
+
+struct S {
+  int a[8] __attribute__((aligned(8))); // no-warning
+};
+
+struct T {
+  int a[4] __attribute__((aligned(16))); // expected-warning {{requesting an alignment of 16 bytes or greater for struct members is not binary compatible with AIX XL 16.1 and older}}
+};
+
+struct U {
+  int a[2] __attribute__((aligned(32))); // expected-warning {{requesting an alignment of 16 bytes or greater for struct members is not binary compatible with AIX XL 16.1 and older}}
+};
+
+int a[8] __attribute__((aligned(8)));  // no-warning
+int b[4] __attribute__((aligned(16))); // no-warning
+int c[2] __attribute__((aligned(32))); // no-warning