diff --git a/src/testdir/test64.in b/src/testdir/test64.in
index 7890924..4d892af 100644
--- a/src/testdir/test64.in
+++ b/src/testdir/test64.in
@@ -361,6 +361,7 @@
 :call add(tl, [2, '\(\i\+\) \1', ' abc abc', 'abc abc', 'abc'])
 :call add(tl, [2, '\(\i\+\) \1', 'xgoo goox', 'goo goo', 'goo'])
 :call add(tl, [2, '\(a\)\(b\)\(c\)\(dd\)\(e\)\(f\)\(g\)\(h\)\(i\)\1\2\3\4\5\6\7\8\9', 'xabcddefghiabcddefghix', 'abcddefghiabcddefghi', 'a', 'b', 'c', 'dd', 'e', 'f', 'g', 'h', 'i'])
+:call add(tl, [2, '\(\d*\)a \1b', ' a b ', 'a b', ''])
 :"
 :"""" Look-behind with limit
 :call add(tl, [2, '<\@<=span.', 'xxspanxx<spanyyy', 'spany'])
diff --git a/src/testdir/test64.ok b/src/testdir/test64.ok
index 31baa4f..0e2f772 100644
--- a/src/testdir/test64.ok
+++ b/src/testdir/test64.ok
@@ -815,6 +815,9 @@
 OK 0 - \(a\)\(b\)\(c\)\(dd\)\(e\)\(f\)\(g\)\(h\)\(i\)\1\2\3\4\5\6\7\8\9
 OK 1 - \(a\)\(b\)\(c\)\(dd\)\(e\)\(f\)\(g\)\(h\)\(i\)\1\2\3\4\5\6\7\8\9
 OK 2 - \(a\)\(b\)\(c\)\(dd\)\(e\)\(f\)\(g\)\(h\)\(i\)\1\2\3\4\5\6\7\8\9
+OK 0 - \(\d*\)a \1b
+OK 1 - \(\d*\)a \1b
+OK 2 - \(\d*\)a \1b
 OK 0 - <\@<=span.
 OK 1 - <\@<=span.
 OK 2 - <\@<=span.