diff --git a/emacs/mu4e-proc.el b/emacs/mu4e-proc.el
index dcc8af60..c746d349 100644
--- a/emacs/mu4e-proc.el
+++ b/emacs/mu4e-proc.el
@@ -123,7 +123,7 @@ process."
   "Start the mu server process."
   ;; TODO: add version check
   (unless (file-executable-p mu4e-mu-binary)
-    (error (format "%S not found" mu4e-mu-binary)))
+    (error (format "`mu4e-mu-binary' (%S) not found" mu4e-mu-binary)))
   (let* ((process-connection-type nil) ;; use a pipe
 	  (args '("server"))
 	  (args (append args (when mu4e-mu-home