diff --git a/pkgs/build-support/fetchgit/nix-prefetch-git b/pkgs/build-support/fetchgit/nix-prefetch-git
index a15c1850d822..9b330d821f85 100755
--- a/pkgs/build-support/fetchgit/nix-prefetch-git
+++ b/pkgs/build-support/fetchgit/nix-prefetch-git
@@ -68,7 +68,7 @@ for arg; do
             --builder) builder=true;;
             --help) usage; exit;;
             *)
-                argi=$((argi++))
+                : $((++argi))
                 case $argi in
                     1) url=$arg;;
                     2) rev=$arg;;