diff --git a/src/caosdb/connection/connection.py b/src/caosdb/connection/connection.py
index bde67069b6a2d8cf44e922cfdd7879d8ab7d675e..a051b8b9dcf5a13ed674184e661da7a281be65c9 100644
--- a/src/caosdb/connection/connection.py
+++ b/src/caosdb/connection/connection.py
@@ -75,7 +75,7 @@ class _WrappedHTTPResponse(CaosDBHTTPResponse):
         return self.response.status_code
 
     def read(self, size=None):
-        if size=None or size = 0:
+        if size is None or size = 0:
             result = b''
             for chunk in self.response.iter_content(chunk_size=1024):
                 result = result + chunk