diff --git a/pkgs/stdenv/generic/setup.sh b/pkgs/stdenv/generic/setup.sh
index 1ed905db363..84d499696c9 100644
--- a/pkgs/stdenv/generic/setup.sh
+++ b/pkgs/stdenv/generic/setup.sh
@@ -669,7 +669,7 @@ patchShebangs() {
     local newInterpreterLine
 
     for f in $(find "$dir" -type f -perm +0100); do
-        if [ $(head -1 "$f" | head -c +2) != '#!' ]; then
+        if [ "$(head -1 "$f" | head -c +2)" != '#!' ]; then
             # missing shebang => not a script
             continue
         fi