diff --git a/baselines/common/vec_env/subproc_vec_env.py b/baselines/common/vec_env/subproc_vec_env.py
index 134e371..e040e3d 100644
--- a/baselines/common/vec_env/subproc_vec_env.py
+++ b/baselines/common/vec_env/subproc_vec_env.py
@@ -111,7 +111,6 @@ def _flatten_obs(obs):
     assert len(obs) > 0
 
     if isinstance(obs[0], dict):
-        import collections
         keys = obs[0].keys()
         return {k: np.stack([o[k] for o in obs]) for k in keys}
     else: