diff --git a/match.c b/match.c
index 5c78ce38..a1775b27 100644
--- a/match.c
+++ b/match.c
@@ -221,7 +221,7 @@ static void hash_search(int f,struct sum_struct *s,
 
     /* Trim off the first byte from the checksum */
     map = window_ptr(buf,offset,k+1);
-    s1 -= map[0] + 1;
+    s1 -= map[0] + CHAR_OFFSET;
     s2 -= k * (map[0]+CHAR_OFFSET);
 
     /* Add on the next byte (if there is one) to the checksum */