diff --git a/synapse/metrics/metric.py b/synapse/metrics/metric.py
index fbba94e63..f421e7a93 100644
--- a/synapse/metrics/metric.py
+++ b/synapse/metrics/metric.py
@@ -71,7 +71,8 @@ class BaseMetric(object):
         """Render this metric for a single set of labels
 
         Args:
-            label_values (list[str]): values for each of the labels
+            label_values (list[object]): values for each of the labels,
+                (which get stringified).
             value: value of the metric at with these labels
 
         Returns:
@@ -324,4 +325,4 @@ def _escape_character(m):
 def _escape_label_value(value):
     """Takes a label value and escapes quotes, newlines and backslashes
     """
-    return re.sub(r"([\n\"\\])", _escape_character, value)
+    return re.sub(r"([\n\"\\])", _escape_character, str(value))