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
@@ -14,6 +14,7 @@
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/MacroBuilder.h"
 #include "clang/Basic/TargetBuiltins.h"
+#include "llvm/Support/Host.h"
 
 using namespace clang;
 using namespace clang::targets;
@@ -301,6 +302,11 @@
     Builder.defineMacro("__LONGDOUBLE64");
   }
 
+  if (llvm::Triple(llvm::sys::getProcessTriple()).isOSAIX() &&
+      getTriple().isOSAIX()) {
+    Builder.defineMacro("__HOS_AIX__");
+  }
+
   // Define this for elfv2 (64-bit only) or 64-bit darwin.
   if (ABI == "elfv2" ||
       (getTriple().getOS() == llvm::Triple::Darwin && PointerWidth == 64))
diff --git a/clang/test/Preprocessor/host-aix.c b/clang/test/Preprocessor/host-aix.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Preprocessor/host-aix.c
@@ -0,0 +1,3 @@
+// REQUIRES: system-aix
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX %s
+// PPC-AIX:#define __HOS_AIX__ 1
diff --git a/clang/test/Preprocessor/not-host-aix.c b/clang/test/Preprocessor/not-host-aix.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Preprocessor/not-host-aix.c
@@ -0,0 +1,3 @@
+// UNSUPPORTED: system-aix
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=powerpc-ibm-aix7.1.0.0 -fno-signed-char < /dev/null | FileCheck -match-full-lines -check-prefix PPC-AIX %s
+// PPC-AIX-NOT:#define __HOS_AIX__ 1