diff --git a/pkgs/racket-test-core/tests/racket/submodule.rktl b/pkgs/racket-test-core/tests/racket/submodule.rktl
index f3bb4f8a84..2bfdbced5e 100644
--- a/pkgs/racket-test-core/tests/racket/submodule.rktl
+++ b/pkgs/racket-test-core/tests/racket/submodule.rktl
@@ -636,7 +636,7 @@
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Directory for testing
 
-(define temp-dir (make-temporary-file "submodule-tests-~s" 'directory))
+(define temp-dir (make-temporary-file "submodule-tests-~a" 'directory))
 
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Check submodule resolution of relative paths: