diff --git a/Dockerfile b/Dockerfile
index a0e34ce..06c6a9a 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM gliderlabs/alpine:edge
+FROM alpine:3.13.2
 
 RUN apk --update add \
   ca-certificates \
diff --git a/README.md b/README.md
index 801b97e..0014749 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,8 @@ It will accept a regular expression as determined by [egrep](http://linuxcommand
 * `rebuild_phrase`: *Optional (default: test this please).* Regular expression as determined by [egrep](http://linuxcommand.org/man_pages/egrep1.html) will match all comments in pull request overview.
 If a match is found the pull request will be rebuilt.
 
+* `debug`: *Optional (default: false).* If set to `true` the bash tracing (`set -x`) will be enabled for the `in`, `out` and `check` scripts.
+
 ## Behavior
 
 ### `check`: Search for pull requests to build.
@@ -131,6 +133,7 @@ resources:
     username: {{bitbucket-username}}
     password: {{bitbucket-password}}
     uri: https://bitbucket.exemple.net/scm/exemple-project/exemple-repo.git
+    debug: true
 
 jobs:
 - name: test pull request
diff --git a/assets/check b/assets/check
index 4f71355..da5a33c 100755
--- a/assets/check
+++ b/assets/check
@@ -24,6 +24,12 @@ payload=$(tmpfile request)
 
 cat > "$payload" <&0
 
+enable_debug=$(jq -r '.source.debug // false' < ${payload})
+if [ "${enable_debug}" = "true" ]; then
+  echo "Enable debug mode"
+  set -x
+fi
+
 log "Configuring git credentials"
 load_pubkey "$payload"
 
@@ -68,7 +74,7 @@ pull_requests=$(jq -r '.[] | [.id, .fromRef.latestCommit, .toRef.latestCommit, .
 if [ -n "$pull_requests" ]; then
   # Check if the current version is still valid
   if [[ "$current_change" -gt 0 ]] && (jq -e --argjson version "$current_version" '.[] | select(
-    .id == (($version.id//0)|tonumber) 
+    .id == (($version.id//0)|tonumber)
     and .fromRef.latestCommit == $version.from
     and .toRef.latestCommit == $version.to)' > /dev/null <<< "$pull_requests_json"); then
       versions="[$current_version]"
diff --git a/assets/helpers/git.sh b/assets/helpers/git.sh
index 8529fdf..d772447 100644
--- a/assets/helpers/git.sh
+++ b/assets/helpers/git.sh
@@ -103,9 +103,11 @@ pullrequest_metadata() {
   # $1: pull request number
   # $2: pull request repository
   # $3: skip ssl verification
+  # $4: source_commit
+  # $5: target_commit
 
-  local source_commit=$(git rev-list --parents -1 $(git rev-parse HEAD) | awk '{print $3}')
-  local target_commit=$(git rev-list --parents -1 $(git rev-parse HEAD) | awk '{print $2}')
+  local source_commit=$4
+  local target_commit=$5
 
   jq -n "[]" | \
     add_pullrequest_metadata_basic "$1" "$2" "$3" | \
diff --git a/assets/in b/assets/in
index 6369e98..aa2a6d1 100755
--- a/assets/in
+++ b/assets/in
@@ -30,6 +30,12 @@ payload=$(tmpfile request)
 
 cat > "$payload" <&0
 
+enable_debug=$(jq -r '.source.debug // false' < ${payload})
+if [ "${enable_debug}" = "true" ]; then
+  log "Enable debug mode"
+  set -x
+fi
+
 load_pubkey "$payload"
 configure_credentials "$payload"
 
@@ -48,6 +54,27 @@ prq_id=$(jq -r '.version.id // ""' < "$payload")
 prq_date=$(jq -r '.version.date // ""' < "$payload")
 prq_change=$(jq -r '.version.change // ""' < "$payload")
 
+# parse uri and retrieve host
+uri_parser "$uri"
+repo_host="${uri_schema}://${uri_address}"
+repo_host=${repo_host}$(getBasePathOfBitbucket)
+
+# determine repository name for calling REST api
+repo_name=$(basename "$uri" | sed "s/.git$//")
+repo_project=$(basename $(dirname "$uri"))
+
+# verify target branch of prq
+prq=$(bitbucket_pullrequest "$repo_host" "$repo_project" "$repo_name" "$prq_id" "" "$skip_ssl_verification")
+
+prq_from=$(echo "$prq" | jq -r '.fromRef.latestCommit')
+prq_from_branch=$(echo "$prq" | jq -r '.fromRef.displayId')
+prq_target=$(echo "$prq" | jq -r '.toRef.latestCommit')
+prq_target_branch=$(echo "$prq" | jq -r '.toRef.displayId')
+
+log "Detected branches"
+log "From: ${prq_from_branch} (${prq_from})"
+log "Target: ${prq_target_branch} (${prq_target})"
+
 configure_git_ssl_verification "$skip_ssl_verification"
 configure_git_global "${git_config_payload}"
 
@@ -66,14 +93,12 @@ if test "$depth" -gt 0 2> /dev/null; then
   depthflag="--depth $depth"
 fi
 
-branch="pull-requests/${prq_id}/merge"
-
 log "Cloning $uri in $destination"
 git clone $depthflag "$uri" "$destination"
 cd "$destination"
 
-git fetch $depthflag origin "+refs/${branch}:refs/remotes/origin/${branch}"
-git checkout -B $branch origin/$branch
+git fetch $depthflag origin "${prq_from_branch}"
+git checkout -B "${prq_from_branch}" "origin/${prq_from_branch}"
 
 ref=$(git rev-parse HEAD)
 
@@ -119,49 +144,33 @@ if [ "$disable_git_lfs" != "true" ]; then
   git submodule foreach "git lfs fetch && git lfs checkout"
 fi
 
-# calculate source and target commit
-source_commit=$(git rev-list --parents -1 $ref | awk '{print $3}')
-target_commit=$(git rev-list --parents -1 $ref | awk '{print $2}')
-
-if [ -z "$source_commit" ]; then
+if [ -z "$prq_from" ]; then
   log "Unable to determine source commit from merge commit $ref. Please verify depth configuration."
   exit 1
 fi
 
-if [ -z "$target_commit" ]; then
+if [ -z "$prq_target" ]; then
   log "Unable to determine target commit from merge commit $ref. Please verify depth configuration."
   exit 1
 fi
 
-# parse uri and retrieve host
-uri_parser "$uri"
-repo_host="${uri_schema}://${uri_address}"
-repo_host=${repo_host}$(getBasePathOfBitbucket)
-
-# determine repository name for calling REST api
-repo_name=$(basename "$uri" | sed "s/.git$//")
-repo_project=$(basename $(dirname "$uri"))
-
-# verify target branch of prq
-prq=$(bitbucket_pullrequest "$repo_host" "$repo_project" "$repo_name" "$prq_id" "" "$skip_ssl_verification")
-
 if [ "$prq" != "ERROR" ]; then
-  branch=$(echo "$prq" | jq -r '.fromRef.displayId')
+  from_branch=$(echo "$prq" | jq -r '.fromRef.displayId')
 fi
 
-
 # expose configuration of pull request that can be used in container
 git config --add pullrequest.id $prq_id
-git config --add pullrequest.source $source_commit
-git config --add pullrequest.target $target_commit
+git config --add pullrequest.source $prq_from
+git config --add pullrequest.target $prq_target
 git config --add pullrequest.merge $ref
 git config --add pullrequest.date "$prq_date"
 git config --add pullrequest.change "$prq_change"
-git config --add pullrequest.branch "$branch"
+git config --add pullrequest.branch "$from_branch"
+git config --add pullrequest.targetbranch "$prq_target_branch"
 
 jq -n \
   --argjson version "$(jq '.version' < "$payload")" \
-  --argjson metadata "$(pullrequest_metadata "$prq_id" "$uri" "$skip_ssl_verification")" \
+  --argjson metadata "$(pullrequest_metadata "$prq_id" "$uri" "$skip_ssl_verification" "$prq_from" "$prq_target")" \
 '{
   version: $version,
   metadata: $metadata
diff --git a/assets/out b/assets/out
index f0f5db6..f67fa30 100755
--- a/assets/out
+++ b/assets/out
@@ -30,6 +30,12 @@ payload=$(tmpfile request)
 
 cat > "$payload" <&0
 
+enable_debug=$(jq -r '.source.debug // false' < ${payload})
+if [ "${enable_debug}" = "true" ]; then
+  echo "Enable debug mode"
+  set -x
+fi
+
 load_pubkey "$payload"
 configure_credentials "$payload"
 
@@ -113,8 +119,8 @@ case "$status" in
 esac
 
 # set build status on commit in bitbucket, this has to be the latest source commit or the pull request won't pick it up
-source_commit=$(git rev-list --parents -1 $merge_commit | awk '{print $3}')
-target_commit=$(git rev-list --parents -1 $merge_commit | awk '{print $2}')
+source_commit=$(git config --get pullrequest.source)
+target_commit=$(git config --get pullrequest.target)
 
 # determine repository name for calling REST api
 repo_name=$(basename "$uri" | sed "s/.git$//")
@@ -196,5 +202,5 @@ jq -n "{
     date: \"$prq_verify_date\",
     change: \"$prq_change\"
   },
-  metadata: $(pullrequest_metadata "$prq_number" "$uri" "$skip_ssl_verification")
+  metadata: $(pullrequest_metadata "$prq_number" "$uri" "$skip_ssl_verification" "$source_commit" "$target_commit")
 }" >&3