Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -16448,7 +16448,22 @@
     bool MSBitfieldViolation =
         Value.ugt(TypeStorageSize) &&
         (IsMsStruct || Context.getTargetInfo().getCXXABI().isMicrosoft());
-    if (CStdConstraintViolation || MSBitfieldViolation) {
+
+    bool AIXBitfieldViolation = false;
+    if (const BuiltinType *BTy = FieldTy.getTypePtr()->getAs<BuiltinType>()) {
+      if ((BTy->getKind() == BuiltinType::ULongLong ||
+           BTy->getKind() == BuiltinType::LongLong) &&
+          (unsigned)Value.getZExtValue() > 32 &&
+          Context.getTargetInfo().getTriple().isArch32Bit() &&
+          Context.getTargetInfo().getTriple().getOS() == llvm::Triple::AIX) {
+        AIXBitfieldViolation = true;
+        TypeStorageSize = 32;
+        TypeWidth = 32;
+      }
+    }
+
+    if (CStdConstraintViolation || MSBitfieldViolation ||
+        AIXBitfieldViolation) {
       unsigned DiagWidth =
           CStdConstraintViolation ? TypeWidth : TypeStorageSize;
       if (FieldName)
Index: clang/test/Layout/aix-oversized-bitfield.cpp
===================================================================
--- /dev/null
+++ clang/test/Layout/aix-oversized-bitfield.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -fsyntax-only -verify -x c++ %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -fdump-record-layouts \
+// RUN:     -fsyntax-only %s | \
+// RUN:   FileCheck --check-prefix=CHECK64 %s
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -fdump-record-layouts \
+// RUN:     -fsyntax-only -x c++ %s | \
+// RUN:   FileCheck --check-prefix=CHECK64 %s
+
+struct A {
+  long long l : 64; // expected-error{{width of bit-field 'l' (64 bits) exceeds size of its type (32 bits)}}
+};
+
+int a = sizeof(A);
+
+// CHECK64:      *** Dumping AST Record Layout
+// CHECK64-NEXT:          0 | struct A
+// CHECK64-NEXT:     0:0-63 |   long long l
+// CHECK64-NEXT:            | [sizeof=8, dsize=8, align=8, preferredalign=8,
+// CHECK64-NEXT:            |  nvsize=8, nvalign=8, preferrednvalign=8]