diff --git a/tox.ini b/tox.ini
index 9b0f71038..af10270ca 100644
--- a/tox.ini
+++ b/tox.ini
@@ -74,6 +74,8 @@ commands =
 
          tahoe --version
 
+	 python -c "import sys; print('sys.stdout.encoding: {}'.format(sys.stdout.encoding))"
+
          # Run tests with -b to catch bugs like `"%s" % (some_bytes,)`. -b makes
          # Python emit BytesWarnings, and warnings configuration in
          # src/allmydata/tests/__init__.py turns allmydata's BytesWarnings into