diff --git a/src/octoprint/util/comm_acc.py b/src/octoprint/util/comm_acc.py
index 53ff8bce..e8ccad21 100644
--- a/src/octoprint/util/comm_acc.py
+++ b/src/octoprint/util/comm_acc.py
@@ -1753,7 +1753,7 @@ class MachineCom(object):
 					continue
 
 				# wait until we have something in the queue
-				string =  "qsize = " % self._send_queue.qsize()
+				string =  "qsize = %s" % self._send_queue.qsize()
 				self._log(string)
 				entry = self._send_queue.get()