diff --git a/pandora_upload/__init__.py b/pandora_upload/__init__.py
index aca4944..2b1940a 100755
--- a/pandora_upload/__init__.py
+++ b/pandora_upload/__init__.py
@@ -59,19 +59,21 @@ def main():
                 print('\ninvalid metadata argument, format is -m "key=value"')
                 sys.exit(1)
             k, v = m.split('=', 1)
+            if v[0] == '[' and v[-1] == ']':
+                v = [v[1:-1]]
             if k in meta:
                 if isinstance(meta[k], str):
                     meta[k] = [meta[k]]
-                meta[k].append(v)
-            elif v[0] == '[' and v[-1] == ']':
-                meta[k] = v[1:-1]
+                if isinstance(v, list):
+                    meta[k].update(v)
+                else:
+                    meta[k].append(v)
             else:
                 meta[k] = v
     files = opts.files
     if not files:
         parser.print_help()
         sys.exit(1)
-
     id = upload(opts.api_url, files, meta)
     print(id)