diff --git a/sprintf.rkt b/sprintf.rkt
index fbc3337..aca4776 100644
--- a/sprintf.rkt
+++ b/sprintf.rkt
@@ -35,7 +35,7 @@
                )
           (when (eq? kind 's)
             (error "argument is a number, but string expected"))
-          (let ((r (~r arg #:pad-string pad-str #:min-width min-width #:precision precision #:base base)))
+          (let ((r (~r arg #:pad-string pad-str #:min-width min-width #:precision (list '= precision) #:base base)))
             (if (eq? adjust 'left)
                 (let ((r-trim (string-trim r)))
                   (string-append r-trim