diff --git a/hnn_core/network.py b/hnn_core/network.py
index 75b57f8c2..a9dd81836 100644
--- a/hnn_core/network.py
+++ b/hnn_core/network.py
@@ -1210,7 +1210,7 @@ def drop(self, probability):
         """
         _validate_type(probability, float, 'probability')
         if probability <= 0.0 or probability >= 1.0:
-            raise ValueError('probability must be in the range [0,1]')
+            raise ValueError('probability must be in the range (0,1)')
         # Flatten connections into a list of targets.
         all_connections = np.concatenate(
             [target_src_pair for