diff --git a/ui/fixtures/cmd.basic.json b/ui/fixtures/cmd.basic.json
index f6caaeb..c3a6106 100644
--- a/ui/fixtures/cmd.basic.json
+++ b/ui/fixtures/cmd.basic.json
@@ -67,6 +67,19 @@
 	"cmd": [ "list", "newfile.txt" ],
 	"stdout_re": "dc:creator:\tJohn-Mark Gurney\nhashes:\tsha512:90f8342520f0ac57fb5a779f5d331c2fa87aa40f8799940257f9ba619940951e67143a8d746535ed0284924b2b7bc1478f095198800ba96d01847d7b56ca465c\nsig:\t.*\ntag:\t\n"
 },
+{
+	"title": "add duplicate ms:tag's",
+	"cmd": [ "modify", "+ms:tag=foo", "+ms:tag=foo", "newfile.txt" ]
+},
+{
+	"title": "but dup tags are not dup'd",
+	"cmd": [ "list", "newfile.txt" ],
+	"stdout_re": "dc:creator:\tJohn-Mark Gurney\nhashes:\tsha512:90f8342520f0ac57fb5a779f5d331c2fa87aa40f8799940257f9ba619940951e67143a8d746535ed0284924b2b7bc1478f095198800ba96d01847d7b56ca465c\nms:tag:\tfoo\nsig:\t.*\ntag:\t\n"
+},
+{
+	"title": "drop ms:tag",
+	"cmd": [ "modify", "-ms:tag=foo", "newfile.txt" ]
+},
 {
 	"title": "add tag",
 	"cmd": [ "modify", "+dc:creator=Another user", "newfile.txt" ]
diff --git a/ui/medashare/cli.py b/ui/medashare/cli.py
index 2339f6a..7ce9392 100644
--- a/ui/medashare/cli.py
+++ b/ui/medashare/cli.py
@@ -253,6 +253,8 @@ class MDBase(object):
 class MetaData(MDBase):
 	_type = 'metadata'
 
+	_uniq_properties = set([ 'ms:tag' ])
+
 class Identity(MDBase):
 	_type = 'identity'
 
@@ -873,8 +875,14 @@ def cmd_modify(options):
 					obj[key].remove(v)
 
 			# add tags
+			uniqify = set()
 			for k, v in adds:
 				obj.setdefault(k, []).append(v)
+				if k in j._uniq_properties:
+					uniqify.add(k)
+
+			for k in uniqify:
+				obj[k] = list(set(obj[k]))
 
 			#print('a:', repr(obj), file=_real_stderr)
 			del obj['modified']