diff --git a/prometheus_client/exposition.py b/prometheus_client/exposition.py
index 6a2db157..a15a4ef8 100644
--- a/prometheus_client/exposition.py
+++ b/prometheus_client/exposition.py
@@ -75,7 +75,7 @@ def sample_line(line):
         if line.labels:
             labelstr = '{{{0}}}'.format(','.join(
                 ['{0}="{1}"'.format(
-                    k, v.replace('\\', r'\\').replace('\n', r'\n').replace('"', r'\"'))
+                    k, str(v).replace('\\', r'\\').replace('\n', r'\n').replace('"', r'\"'))
                     for k, v in sorted(line.labels.items())]))
         else:
             labelstr = ''