diff --git a/mercurial/bdiff.c b/mercurial/bdiff.c
--- a/mercurial/bdiff.c
+++ b/mercurial/bdiff.c
@@ -184,7 +184,7 @@ static int longest_match(struct bdiff_li
 				mj = j;
 				mk = k;
 			} else if (k == mk) {
-				if (i > mi && i <= half) {
+				if (i > mi && i <= half && j > b1) {
 					/* same match but closer to half */
 					mi = i;
 					mj = j;
diff --git a/tests/test-bdiff.py b/tests/test-bdiff.py
--- a/tests/test-bdiff.py
+++ b/tests/test-bdiff.py
@@ -88,7 +88,7 @@ print("Diff 1 to 3 lines - preference fo
 showdiff('a\n', 'a\n' * 3)
 print("Diff 1 to 5 lines - preference for appending:")
 showdiff('a\n', 'a\n' * 5)
-print("Diff 3 to 1 lines - preference for balanced recursion:")
+print("Diff 3 to 1 lines - preference for removing trailing lines:")
 showdiff('a\n' * 3, 'a\n')
-print("Diff 5 to 1 lines - preference for balanced recursion:")
+print("Diff 5 to 1 lines - preference for removing trailing lines:")
 showdiff('a\n' * 5, 'a\n')
diff --git a/tests/test-bdiff.py.out b/tests/test-bdiff.py.out
--- a/tests/test-bdiff.py.out
+++ b/tests/test-bdiff.py.out
@@ -68,17 +68,15 @@ showdiff(
   'a\na\na\na\na\n'):
  'a\n'
  2 2 '' -> 'a\na\na\na\n'
-Diff 3 to 1 lines - preference for balanced recursion:
+Diff 3 to 1 lines - preference for removing trailing lines:
 showdiff(
   'a\na\na\n',
   'a\n'):
- 0 2 'a\n' -> ''
  'a\n'
- 4 6 'a\n' -> ''
-Diff 5 to 1 lines - preference for balanced recursion:
+ 2 6 'a\na\n' -> ''
+Diff 5 to 1 lines - preference for removing trailing lines:
 showdiff(
   'a\na\na\na\na\n',
   'a\n'):
- 0 4 'a\na\n' -> ''
  'a\n'
- 6 10 'a\na\n' -> ''
+ 2 10 'a\na\na\na\n' -> ''