diff --git a/pkgs/development/libraries/fltk/default.nix b/pkgs/development/libraries/fltk/default.nix
index 433c071a52d7..3181bb038ea8 100644
--- a/pkgs/development/libraries/fltk/default.nix
+++ b/pkgs/development/libraries/fltk/default.nix
@@ -185,7 +185,7 @@ stdenv.mkDerivation (finalAttrs: {
 
   postFixup = ''
     substituteInPlace $out/bin/fltk-config \
-      --replace "/$out/" "/"
+      --replace-fail "/$out/" "/"
   '';
 
   meta = {