diff --git a/swh/model/hypothesis_strategies.py b/swh/model/hypothesis_strategies.py
index 3e006c8afaae1d5ec8f51c6135ae7023fbabc062..61c55e11415026c0d7ca1f948fc1b93a778ed0cf 100644
--- a/swh/model/hypothesis_strategies.py
+++ b/swh/model/hypothesis_strategies.py
@@ -143,7 +143,7 @@ def contents(draw):
 
 
 def branch_names():
-    return binary()
+    return binary(min_size=1)
 
 
 def branch_targets_object():