diff --git a/cascading-pr.sh b/cascading-pr.sh
index 2e42a83..08c44a5 100755
--- a/cascading-pr.sh
+++ b/cascading-pr.sh
@@ -100,7 +100,7 @@ EOF
 }
 
 function close_pr() {
-    local direction=$1
+    local direction=destination
 
     if test "$(pr_state ${direction})" = "open"; then
 	log_info "closing $(pr_url ${direction})"
@@ -147,9 +147,14 @@ function pr_number() {
     pr $1 | jq --raw-output .number
 }
 
-function pr_head() {
+function pr_sha() {
     pr_get $1
-    pr $1 | jq --raw-output .head.ref
+    merged=$(pr $1 | jq --raw-output .merged)
+    if "$merged"; then
+	pr $1 | jq --raw-output .merge_commit_sha
+    else
+	pr $1 | jq --raw-output .head.sha
+    fi
 }
 
 function pr_merged() {
@@ -158,19 +163,20 @@ function pr_merged() {
 }
 
 function upsert_clone() {
-    local direction=$1 branch=$2 clone=$3
+    local direction=$1 ref="$2" sha="$3" clone=$4
 
-    local fetch=true
     if ! test -d $TMPDIR/$direction; then
-	git -c credential.helper="store --file=$TMPDIR/$direction.git-credentials" clone $clone -b $branch $TMPDIR/$direction
-	fetch=false
+	git -c credential.helper="store --file=$TMPDIR/$direction.git-credentials" clone $clone $TMPDIR/$direction
     fi
     (
 	cd $TMPDIR/$direction
-	git config credential.helper "store --file=$TMPDIR/$direction.git-credentials"
-	if $fetch; then
-	    git fetch origin
+	if test "$ref"; then
+	    git switch -c $direction origin/$ref
 	fi
+	if test "$sha"; then
+	    git switch -c $direction $sha
+	fi
+	git config credential.helper "store --file=$TMPDIR/$direction.git-credentials"
 	git config user.email cascading-pr@example.com
 	git config user.name cascading-pr
     )
@@ -190,7 +196,7 @@ function push() {
 	cd $TMPDIR/$direction
 	git add .
 	if git commit -m 'cascading-pr update'; then
-	    git push --force origin $branch
+	    git push --force origin $direction:$branch
 	    git rev-parse HEAD > ../$direction.sha
 	    log_info "pushed"
 	else
@@ -206,8 +212,8 @@ function wait_destination_ci() {
 }
 
 function update() {
-    upsert_clone origin ${options[origin_head]} ${options[origin_clone]}
-    upsert_clone destination ${options[destination_head]} ${options[destination_clone]}
+    upsert_clone origin "${options[origin_head]}" "${options[origin_sha]}" ${options[origin_clone]}
+    upsert_clone destination "${options[destination_head]}" "${options[destination_sha]}" ${options[destination_clone]}
     (
 	cd $TMPDIR/origin
 	${options[update]} $TMPDIR/destination $TMPDIR/destination-pr.json $TMPDIR/origin-pr.json
@@ -237,7 +243,8 @@ function finalize_options() {
     options[origin_scheme]=$(scheme ${options[origin_url]})
     options[origin_host_port]=$(host_port ${options[origin_url]})
     set_clone origin
-    options[origin_head]=$(pr_head origin)
+    options[origin_head]=
+    options[origin_sha]=$(pr_sha origin)
     options[destination_api]=${options[destination_url]}/api/v1/repos/${options[destination_repo]}
     options[destination_scheme]=$(scheme ${options[destination_url]})
     options[destination_host_port]=$(host_port ${options[destination_url]})
@@ -245,6 +252,7 @@ function finalize_options() {
     options[destination_base]=${options[destination_branch]}
     : ${options[prefix]:=${options[origin_repo]}}
     options[destination_head]=${options[prefix]}-${options[origin_pr]}
+    options[destination_sha]=
 }
 
 function run() {
@@ -274,7 +282,7 @@ function run() {
 	    else
 		log_info "PR is closed, close the cascade PR and remove the branch"
 		repo_login ${options[destination_repo]}
-		close_pr destination
+		close_pr
 	    fi
 	    ;;
 	*)