diff --git a/gnu/system/image.scm b/gnu/system/image.scm
index 251615a757..2cd035e4e7 100644
--- a/gnu/system/image.scm
+++ b/gnu/system/image.scm
@@ -299,7 +299,7 @@ (define (format->image-type format)
         (raise (condition
                 (&message
                  (message
-                  (format #f (G_ "Unsupported image type ~a~%.")
+                  (format #f (G_ "unsupported image type: ~a")
                           format))))))))
 
     (define (partition->dos-type partition)