diff --git a/src/testdir/test69.in b/src/testdir/test69.in
index 75317b4..2510c12 100644
--- a/src/testdir/test69.in
+++ b/src/testdir/test69.in
@@ -180,6 +180,13 @@
 byteidxcomp
 
 STARTTEST
+/^substitute
+:let y = substitute('１２３', '\zs', 'a', 'g')    | put =y
+ENDTEST
+
+substitute
+
+STARTTEST
 :g/^STARTTEST/.,/^ENDTEST/d
 :1;/^Results/,$wq! test.out
 ENDTEST
diff --git a/src/testdir/test69.ok b/src/testdir/test69.ok
index 41cd9d0..af8befb 100644
--- a/src/testdir/test69.ok
+++ b/src/testdir/test69.ok
@@ -160,3 +160,7 @@
 [0, 1, 3, 4, -1]
 [0, 1, 2, 4, 5, -1]
 
+
+substitute
+a１a２a３a
+