diff --git a/lib/getpass.h b/lib/getpass.h
index c90780bb238ad9389460244ad363113e8b5e6379..249a26ec6ed682bd6aef6691782f446965a26be1 100644
--- a/lib/getpass.h
+++ b/lib/getpass.h
@@ -29,7 +29,7 @@
 /*
  * Returning NULL will abort the continued operation!
  */
-char* getpass_r(char *prompt, char* buffer, size_t buflen );
+char* getpass_r(const char *prompt, char* buffer, size_t buflen );
 #endif
 
 #endif