diff --git a/moulinette/core.py b/moulinette/core.py
index fc147c01..4e1b20f4 100644
--- a/moulinette/core.py
+++ b/moulinette/core.py
@@ -89,13 +89,20 @@ class Translator(object):
 
         """
         if key in self._translations.get(self.locale, {}):
-            return self._translations[self.locale][key].encode('utf-8').format(*args, **kwargs)
+            try:
+                return self._translations[self.locale][key].encode('utf-8').format(*args, **kwargs)
+            except KeyError as e:
+                logger.warning("Failed to format translated string '%s' with error: %s" % (key, e))
 
         if self.default_locale != self.locale and key in self._translations.get(self.default_locale, {}):
             logger.info("untranslated key '%s' for locale '%s'",
                         key, self.locale)
 
-            return self._translations[self.default_locale][key].encode('utf-8').format(*args, **kwargs)
+            try:
+                return self._translations[self.default_locale][key].encode('utf-8').format(*args, **kwargs)
+            except KeyError as e:
+                logger.warning("Failed to format translatable string '%s' with error: %s" % (key, e))
+                return key
 
         logger.exception("unable to retrieve key '%s' for default locale '%s'",
                          key, self.default_locale)