diff --git a/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh b/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh
index 73be2eb5960a..d20895fd12ba 100644
--- a/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh
+++ b/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh
@@ -7,4 +7,4 @@ fixGprProjectDarwinRpath() {
     done
 }
 
-preFixupPhases+=" fixGprProjectDarwinRpath"
+appendToVar preFixupPhases fixGprProjectDarwinRpath