diff --git a/setup/start/collectd/df.py b/setup/start/collectd/df.py
index 9e860ee8d..b0e4d45e5 100644
--- a/setup/start/collectd/df.py
+++ b/setup/start/collectd/df.py
@@ -14,7 +14,7 @@ def read():
     for d in disks:
         device = d[0]
         if 'devicemapper' in d[1] or not device.startswith('/dev/'): continue
-        instance = device[len('/dev/'):].replace('/', '-')
+        instance = device[len('/dev/'):].replace('/', '_') # see #348
 
         try:
             st = os.statvfs(d[1]) # handle disk removal