diff --git a/nilmdb/server/server.py b/nilmdb/server/server.py
index 42d17e1..4712ad3 100644
--- a/nilmdb/server/server.py
+++ b/nilmdb/server/server.py
@@ -227,6 +227,20 @@ class Stream(NilmApp):
                 result[k] = None
         return result
 
+    # Helper for set_metadata and get_metadata
+    def _metadata_helper(self, function, path, data):
+        if not isinstance(data, dict):
+            try:
+                data = dict(json.loads(data))
+            except TypeError as e:
+                raise NilmDBError("can't parse 'data' parameter: " + e.message)
+        for key in data:
+            if not (isinstance(data[key], basestring) or
+                    isinstance(data[key], float) or
+                    isinstance(data[key], int)):
+                raise NilmDBError("metadata values must be a string or number")
+        function(path, data)
+
     # /stream/set_metadata?path=/newton/prep&data=<json>
     @cherrypy.expose
     @cherrypy.tools.json_in()
@@ -235,30 +249,19 @@ class Stream(NilmApp):
     @cherrypy.tools.CORS_allow(methods = ["POST"])
     def set_metadata(self, path, data):
         """Set metadata for the named stream, replacing any existing
-        metadata.  Data can be json-encoded or a plain dictionary (if
-        it was sent as application/json to begin with)"""
-        if not isinstance(data, dict):
-            try:
-                data = dict(json.loads(data))
-            except TypeError as e:
-                raise NilmDBError("can't parse 'data' parameter: " + e.message)
-        self.db.stream_set_metadata(path, data)
+        metadata.  Data can be json-encoded or a plain dictionary."""
+        self._metadata_helper(self.db.stream_set_metadata, path, data)
 
     # /stream/update_metadata?path=/newton/prep&data=<json>
     @cherrypy.expose
     @cherrypy.tools.json_in()
     @cherrypy.tools.json_out()
-    @exception_to_httperror(NilmDBError, LookupError)
+    @exception_to_httperror(NilmDBError, LookupError, ValueError)
     @cherrypy.tools.CORS_allow(methods = ["POST"])
     def update_metadata(self, path, data):
-        """Update metadata for the named stream.  Data
-        should be a json-encoded dictionary"""
-        if not isinstance(data, dict):
-            try:
-                data = dict(json.loads(data))
-            except TypeError as e:
-                raise NilmDBError("can't parse 'data' parameter: " + e.message)
-        self.db.stream_update_metadata(path, data)
+        """Set metadata for the named stream, replacing any existing
+        metadata.  Data can be json-encoded or a plain dictionary."""
+        self._metadata_helper(self.db.stream_update_metadata, path, data)
 
     # /stream/insert?path=/newton/prep
     @cherrypy.expose
diff --git a/tests/test_client.py b/tests/test_client.py
index 8d89bbf..5d4c39e 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -162,6 +162,16 @@ class TestClient(object):
             client.stream_set_metadata("/newton/prep", [1,2,3])
         with assert_raises(ClientError):
             client.stream_update_metadata("/newton/prep", [1,2,3])
+
+        # test wrong types (dict of non-strings)
+        # numbers are OK; they'll get converted to strings
+        client.stream_set_metadata("/newton/prep", { "hello": 1234 })
+        # anything else is not
+        with assert_raises(ClientError):
+            client.stream_set_metadata("/newton/prep", { "world": { 1: 2 } })
+        with assert_raises(ClientError):
+            client.stream_set_metadata("/newton/prep", { "world": [ 1, 2 ] })
+
         client.close()
 
     def test_client_04_insert(self):