diff -Naur a/src/glsl/glcpp/glcpp-parse.y b/src/glsl/glcpp/glcpp-parse.y
--- a/src/glsl/glcpp/glcpp-parse.y	2014-02-16 12:32:19.428189812 +0000
+++ b/src/glsl/glcpp/glcpp-parse.y	2014-02-16 12:35:29.242185663 +0000
@@ -1773,9 +1773,6 @@
 	/* According to the GLSL specification, macro names starting with "__"
 	 * or "GL_" are reserved for future use.  So, don't allow them.
 	 */
-	if (strstr(identifier, "__")) {
-		glcpp_error (loc, parser, "Macro names containing \"__\" are reserved.\n");
-	}
 	if (strncmp(identifier, "GL_", 3) == 0) {
 		glcpp_error (loc, parser, "Macro names starting with \"GL_\" are reserved.\n");
 	}