diff --git a/clang/lib/Headers/unwind.h b/clang/lib/Headers/unwind.h
index 66ede93e6b96..773f3e809334 100644
--- a/clang/lib/Headers/unwind.h
+++ b/clang/lib/Headers/unwind.h
@@ -23,7 +23,8 @@
 
 /* See "Data Definitions for libgcc_s" in the Linux Standard Base.*/
 
-#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >=  1070
+#if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && \
+    __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >=  1070
 /* Starting in OS X Lion the SDK includes a unwind.h. We should just use it. */
 #include_next <unwind.h>
 #else