diff --git a/pkgs/development/libraries/aws-c-common/setup-hook.sh b/pkgs/development/libraries/aws-c-common/setup-hook.sh
index e670f7cf8529..174933621f00 100644
--- a/pkgs/development/libraries/aws-c-common/setup-hook.sh
+++ b/pkgs/development/libraries/aws-c-common/setup-hook.sh
@@ -1,5 +1,5 @@
 addAwsCCommonModuleDir() {
-    cmakeFlags="-DCMAKE_MODULE_PATH=@out@/lib/cmake ${cmakeFlags:-}"
+    prependToVar cmakeFlags "-DCMAKE_MODULE_PATH=@out@/lib/cmake"
 }
 
 postHooks+=(addAwsCCommonModuleDir)