diff --git a/bpttool b/bpttool
index 6b4f56d..31cc508 100755
--- a/bpttool
+++ b/bpttool
@@ -946,7 +946,7 @@
       BptError: If another application-specific error occurs
     """
 
-    partitions, _ = self._read_json([input_file], 'ab_collapse')
+    partitions, _ = self._read_json([input_file], ab_collapse)
 
     part = None
     for p in partitions: