diff --git a/tools/mountstats/mountstats.py b/tools/mountstats/mountstats.py
index 8e129c83..d488f9e1 100755
--- a/tools/mountstats/mountstats.py
+++ b/tools/mountstats/mountstats.py
@@ -333,6 +333,11 @@ class DeviceData:
             found = True
             self.__parse_rpc_line(words)
 
+    def fstype(self):
+        """Return the fstype for the mountpoint
+        """
+        return self.__nfs_data['fstype']
+
     def is_nfs_mountpoint(self):
         """Return True if this is an NFS or NFSv4 mountpoint,
         otherwise return False
@@ -953,73 +958,78 @@ def nfsstat_command(args):
     return 0
 
 def print_iostat_summary(old, new, devices, time):
+    if len(devices) == 0:
+        print('No NFS mount points were found')
+        return
+
     for device in devices:
         stats = DeviceData()
         stats.parse_stats(new[device])
-        if not old or device not in old:
+        if old and device in old:
+            old_stats = DeviceData()
+            old_stats.parse_stats(old[device])
+            if stats.fstype() == old_stats.fstype():
+                stats.compare_iostats(old_stats).display_iostats(time)
+            else: # device is in old, but fstypes are different
+                stats.display_iostats(time)
+        else: # device is only in new
             stats.display_iostats(time)
-        else:
-            if ("fstype autofs" not in str(old[device])) and ("fstype autofs" not in str(new[device])):
-                old_stats = DeviceData()
-                old_stats.parse_stats(old[device])
-                diff_stats = stats.compare_iostats(old_stats)
-                diff_stats.display_iostats(time)
+
+def list_nfs_mounts(givenlist, mountstats):
+    """return a list of NFS mounts given a list to validate or
+       return a full list if the given list is empty -
+       may return an empty list if none found
+    """
+    devicelist = []
+    if len(givenlist) > 0:
+        for device in givenlist:
+            if device in mountstats:
+                stats = DeviceData()
+                stats.parse_stats(mountstats[device])
+                if stats.is_nfs_mountpoint():
+                    devicelist += [device]
+    else:
+        for device, descr in mountstats.items():
+            stats = DeviceData()
+            stats.parse_stats(descr)
+            if stats.is_nfs_mountpoint():
+                devicelist += [device]
+    return devicelist
 
 def iostat_command(args):
     """iostat-like command for NFS mount points
     """
     mountstats = parse_stats_file(args.infile)
-    devices = [os.path.normpath(mp) for mp in args.mountpoints]
+    origdevices = [os.path.normpath(mp) for mp in args.mountpoints]
 
     if args.since:
         old_mountstats = parse_stats_file(args.since)
     else:
         old_mountstats = None
 
-    # make certain devices contains only NFS mount points
-    if len(devices) > 0:
-        check = []
-        for device in devices:
-            stats = DeviceData()
-            try:
-                stats.parse_stats(mountstats[device])
-                if stats.is_nfs_mountpoint():
-                    check += [device]
-            except KeyError:
-                continue
-        devices = check
-    else:
-        for device, descr in mountstats.items():
-            stats = DeviceData()
-            stats.parse_stats(descr)
-            if stats.is_nfs_mountpoint():
-                devices += [device]
-    if len(devices) == 0:
-        print('No NFS mount points were found')
-        return 1
-
     sample_time = 0
 
+    # make certain devices contains only NFS mount points
+    devices = list_nfs_mounts(origdevices, mountstats)
+    print_iostat_summary(old_mountstats, mountstats, devices, sample_time)
+
     if args.interval is None:
-        print_iostat_summary(old_mountstats, mountstats, devices, sample_time)
         return
 
-    if args.count is not None:
-        count = args.count
-        while count != 0:
-            print_iostat_summary(old_mountstats, mountstats, devices, sample_time)
-            old_mountstats = mountstats
-            time.sleep(args.interval)
-            sample_time = args.interval
-            mountstats = parse_stats_file(args.infile)
+    count = args.count
+    while True:
+        if count is not None:
             count -= 1
-    else: 
-        while True:
-            print_iostat_summary(old_mountstats, mountstats, devices, sample_time)
-            old_mountstats = mountstats
-            time.sleep(args.interval)
-            sample_time = args.interval
-            mountstats = parse_stats_file(args.infile)
+            if count == 0:
+                break
+        time.sleep(args.interval)
+        old_mountstats = mountstats
+        sample_time = args.interval
+        mountstats = parse_stats_file(args.infile)
+        # nfs mountpoints may appear or disappear, so we need to
+        # recheck the devices list each time we parse mountstats
+        devices = list_nfs_mounts(origdevices, mountstats)
+        print_iostat_summary(old_mountstats, mountstats, devices, sample_time)
 
     args.infile.close()
     if args.since: