diff --git a/pkgs/top-level/builder-defs.nix b/pkgs/top-level/builder-defs.nix
index e3c27d072120..ea6914eddcb7 100644
--- a/pkgs/top-level/builder-defs.nix
+++ b/pkgs/top-level/builder-defs.nix
@@ -287,7 +287,7 @@ args: with args; with stringsWithDeps; with lib;
 
         patches = getAttr ["patches"] [] args;
 
-        toPatchCommand = s: "cat ${toString s} | patch ${toString patchFlags}";
+        toPatchCommand = s: "cat ${s} | patch ${toString patchFlags}";
 
         doPatch = FullDepEntry (concatStringsSep ";"
                 (map toPatchCommand patches)