diff --git a/src/materials.py b/src/materials.py
index a8dc05b..43d4c65 100755
--- a/src/materials.py
+++ b/src/materials.py
@@ -157,7 +157,7 @@ def get_value(data, element):
   keys = element.split('/')
   for key in keys:
     data = data.get(key)
-  if data and len(data) == 1:
+  if isinstance(data, dict) and data and len(data) == 1:
     data = next(iter(data.values()))
   return data