diff --git a/src/filters/rclchm b/src/filters/rclchm
index b7c4bbaf..1bf45f5b 100755
--- a/src/filters/rclchm
+++ b/src/filters/rclchm
@@ -244,7 +244,7 @@ class rclCHM:
         return (False, "", path, iseof)
 
     def dumpall(self):
-        alltxt=""
+        alltxt=b""
         for pth in self.contents:
             ret,doc,path,iseof = self.extractone(pth)
             if not ret: