diff --git a/lib/Basic/Targets/OSTargets.h b/lib/Basic/Targets/OSTargets.h
index 519a35b06f955b058f1afa4b769381174630dc8e..ca84a875de1427c564a4ff4f56ac955836d3d7cc 100644
--- a/lib/Basic/Targets/OSTargets.h
+++ b/lib/Basic/Targets/OSTargets.h
@@ -505,6 +505,8 @@ protected:
 
     Builder.defineMacro("__rtems__");
     Builder.defineMacro("__ELF__");
+    if (Opts.CPlusPlus)
+      Builder.defineMacro("_GNU_SOURCE");
   }
 
 public:
diff --git a/test/Preprocessor/init.c b/test/Preprocessor/init.c
index 7b742b323428c4c4455a7eac258fd5c006acf535..11f05e6241ec203849ac2307c06c96a28cde06e8 100644
--- a/test/Preprocessor/init.c
+++ b/test/Preprocessor/init.c
@@ -8955,6 +8955,7 @@
 // KFREEBSDI686-DEFINE:#define __GLIBC__ 1
 //
 // RUN: %clang_cc1 -x c++ -triple i686-pc-linux-gnu -fobjc-runtime=gcc -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix GNUSOURCE %s
+// RUN: %clang_cc1 -x c++ -triple sparc-rtems-elf -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix GNUSOURCE %s
 // GNUSOURCE:#define _GNU_SOURCE 1
 //
 // RUN: %clang_cc1 -x c++ -std=c++98 -fno-rtti -E -dM < /dev/null | FileCheck -match-full-lines -check-prefix NORTTI %s