diff --git a/clang/lib/Basic/Targets/PPC.cpp b/clang/lib/Basic/Targets/PPC.cpp
--- a/clang/lib/Basic/Targets/PPC.cpp
+++ b/clang/lib/Basic/Targets/PPC.cpp
@@ -256,6 +256,10 @@
     Builder.defineMacro("__powerpc64__");
     Builder.defineMacro("__ppc64__");
     Builder.defineMacro("__PPC64__");
+  // Also define _ARCH_PPC64 for 32-bit on AIX.
+  } else {
+    if (getTriple().isOSAIX())
+      Builder.defineMacro("_ARCH_PPC64");
   }
 
   // Target properties.
diff --git a/clang/test/Preprocessor/init-ppc.c b/clang/test/Preprocessor/init-ppc.c
--- a/clang/test/Preprocessor/init-ppc.c
+++ b/clang/test/Preprocessor/init-ppc.c
@@ -391,6 +391,7 @@
 // PPC-AIX-NOT:#define __64BIT__ 1
 // PPC-AIX:#define _AIX 1
 // PPC-AIX:#define _ARCH_PPC 1
+// PPC-AIX:#define _ARCH_PPC64 1
 // PPC-AIX:#define _BIG_ENDIAN 1
 // PPC-AIX:#define _IBMR2 1
 // PPC-AIX:#define _LONG_LONG 1