diff --git a/tox.ini b/tox.ini
index aedd87a03f..74ce5f6147 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,6 +18,9 @@ envdir=pytest
 
 
 [testenv:coverage]
+setenv=
+  DISABLE_SQLALCHEMY_CEXT=1
+
 commands=
   python -m pytest \
         --cov=lib/sqlalchemy \