diff --git a/tests/test-backout b/tests/test-backout
--- a/tests/test-backout
+++ b/tests/test-backout
@@ -1,5 +1,7 @@
 #!/bin/sh
 
+HGMERGE=true; export HGMERGE
+
 echo '# basic operation'
 hg init basic
 cd basic