diff --git a/vdirsyncer/cli/fetchparams.py b/vdirsyncer/cli/fetchparams.py
index 9623d7a..59009c9 100644
--- a/vdirsyncer/cli/fetchparams.py
+++ b/vdirsyncer/cli/fetchparams.py
@@ -64,6 +64,10 @@ def _fetch_value(opts, key):
         password_cache[cache_key] = e
         raise
     else:
+        if not rv:
+            raise exceptions.UserError('Empty value for {}, this most likely '
+                                       'indicates an error.'
+                                       .format(key))
         password_cache[cache_key] = rv
         return rv