diff --git a/pkgs/development/interpreters/python/hooks/pip-build-hook.sh b/pkgs/development/interpreters/python/hooks/pip-build-hook.sh
index a58c01ce808c..292f13d30154 100644
--- a/pkgs/development/interpreters/python/hooks/pip-build-hook.sh
+++ b/pkgs/development/interpreters/python/hooks/pip-build-hook.sh
@@ -36,7 +36,7 @@ if [ -z "${dontUsePipBuild-}" ] && [ -z "${buildPhase-}" ]; then
     buildPhase=pipBuildPhase
 fi
 
-if [ -z "$shellHook" ]; then
+if [ -z "${shellHook-}" ]; then
     echo "Using pipShellHook"
     shellHook=pipShellHook
 fi