diff --git a/tools/releasetools/blockimgdiff.py b/tools/releasetools/blockimgdiff.py
index 42007eb..4415e57 100644
--- a/tools/releasetools/blockimgdiff.py
+++ b/tools/releasetools/blockimgdiff.py
@@ -355,7 +355,7 @@
       free_string = []
 
       if self.version == 1:
-        src_str = xf.src_ranges.to_string_raw()
+        src_str = xf.src_ranges.to_string_raw() if xf.src_ranges else ""
       elif self.version >= 2:
 
         #   <# blocks> <src ranges>