diff --git a/productmd/compose.py b/productmd/compose.py
index f9e691b..91c89f4 100644
--- a/productmd/compose.py
+++ b/productmd/compose.py
@@ -143,6 +143,6 @@ def _load_metadata(self, paths, cls):
         obj = cls()
         try:
             obj.load(path)
-        except ValueError:
-            raise RuntimeError('%s is not a valid JSON file.' % path)
+        except ValueError as exc:
+            raise RuntimeError('%s can not be deserialized: %s.' % (path, exc))
         return obj