diff --git a/pkgs/development/interpreters/io/default.nix b/pkgs/development/interpreters/io/default.nix
index f4854c237bd2..4f4880aaca72 100644
--- a/pkgs/development/interpreters/io/default.nix
+++ b/pkgs/development/interpreters/io/default.nix
@@ -18,7 +18,8 @@ stdenv.mkDerivation {
     freeglut libsamplerate pcre libevent libedit yajl
   ];
 
-  cmakeFlags = [ "-DCMAKE_BUILD_TYPE=release" ];
+  # for gcc5; c11 inline semantics breaks the build
+  NIX_CFLAGS_COMPILE = "-fgnu89-inline";
 
   meta = {
     description = "Io programming language";