diff --git a/slate/slate.py b/slate/slate.py
index 1555dea..3549b36 100644
--- a/slate/slate.py
+++ b/slate/slate.py
@@ -117,8 +117,9 @@ class Slate():
             if k in conf:
                 del conf[k]
 
-            while val.find('{') != -1:
-                val = self.expand_vars(val, config=self._config, **kwargs)
+            if type(val, str):
+                while val.find('{') != -1:
+                    val = self.expand_vars(val, config=self._config, **kwargs)
 
             return val
         child = conf.get(keys_arr[0], {})