diff -r e8035cfc9647 src/check.c
--- a/src/check.c	Wed Jun 19 17:41:41 2013 +0200
+++ b/src/check.c	Mon Jul 08 14:46:04 2013 +0200
@@ -654,6 +654,12 @@
                 return PWQ_ERROR_EMPTY_PASSWORD;
         }
 
+        if (user && *user == '\0')
+                user = NULL;
+
+        if (oldpassword && *oldpassword == '\0')
+                oldpassword = NULL;
+
         if (oldpassword && strcmp(oldpassword, password) == 0) {
                 return PWQ_ERROR_SAME_PASSWORD;
         }