diff --git a/kafl_fuzzer/common/util.py b/kafl_fuzzer/common/util.py
index 97310b2..eaa8538 100644
--- a/kafl_fuzzer/common/util.py
+++ b/kafl_fuzzer/common/util.py
@@ -84,11 +84,11 @@ def read_binary_file(filename) -> bytes:
         return f.read()
 
 def find_diffs(data_a: bytes, data_b: bytes) -> Tuple[Optional[int], Optional[int]]:
-    first_diff = None
-    last_diff = None
+    first_diff = 0
+    last_diff = 0
     for i in range(min(len(data_a), len(data_b))):
         if data_a[i] != data_b[i]:
-            if first_diff is None:
+            if first_diff == 0:
                 first_diff = i
             last_diff = i
     return first_diff, last_diff