diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 4e67fbbe96..10f2d17419 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -178,6 +178,7 @@ def cmd(self, cmd):
         cmd = cmd.strip()
         assert cmd != 'q' and cmd != 'quit'
         self._p.stdin.write(cmd + '\n')
+        self._p.stdin.flush()
         return self._read_output()