diff --git a/lib/core/common.py b/lib/core/common.py
index ce75fa6a2..2db4e7ef9 100644
--- a/lib/core/common.py
+++ b/lib/core/common.py
@@ -644,7 +644,10 @@ def filePathToString(filePath):
 
     return strRepl
 
-def singleTimeLogMessage(message, level, flag):
+def singleTimeLogMessage(message, level=logging.WARN, flag=None):
+    if flag is None:
+        flag = hash(message)
+
     if flag not in kb.singleLogFlags:
         kb.singleLogFlags.add(flag)
         logger.log(level, message)
diff --git a/plugins/dbms/mysql/filesystem.py b/plugins/dbms/mysql/filesystem.py
index 7c60a9f7e..e18e2b36a 100644
--- a/plugins/dbms/mysql/filesystem.py
+++ b/plugins/dbms/mysql/filesystem.py
@@ -7,6 +7,7 @@ Copyright (c) 2006-2011 sqlmap developers (http://sqlmap.sourceforge.net/)
 See the file 'doc/COPYING' for copying permission
 """
 
+from lib.core.common import singleTimeLogMessage
 from lib.core.common import randomStr
 from lib.core.data import conf
 from lib.core.data import kb
@@ -94,6 +95,10 @@ class Filesystem(GenericFilesystem):
         if confirm:
             self.askCheckWrittenFile(wFile, dFile, fileType)
 
+        warnMsg = "expect junk characters inside the "
+        warnMsg += "file as a leftover from UNION query"
+        singleTimeLogMessage(warnMsg)
+
     def stackedWriteFile(self, wFile, dFile, fileType, confirm=True):
         debugMsg = "creating a support table to write the hexadecimal "
         debugMsg += "encoded file to"