diff --git a/README b/README
index c9159aca85cad74a16be3fec27cd5241e68b9557..33b1b331d633b9dcee07fb29eae8453277e0a838 100644
--- a/README
+++ b/README
@@ -6,7 +6,8 @@ This version is known to compile with:
  - Coq 8.4pl3
  - SCons 2.0
  - Ocaml 4.01.0
-
+ - GNU C preprocessor 4.7
+ 
 BUILDING INSTRUCTIONS
 ---------------------