diff --git a/tests/test_conflict_resolution_resume.sh b/tests/test_conflict_resolution_resume.sh
index 205b101..b7c1c88 100644
--- a/tests/test_conflict_resolution_resume.sh
+++ b/tests/test_conflict_resolution_resume.sh
@@ -33,7 +33,11 @@ echo "gh $*" >> "$CALLS"
 if [[ "$1 $2" == "pr view" ]]; then
     case "$*" in
         *--json\ labels*)   printf '%s\n' "${MOCK_LABELS:-}";;
-        *--json\ comments*) cat "${MOCK_COMMENTS_FILE:-/dev/null}";;
+        *--json\ comments*)
+            # The comments file stands for our own comments only, so the query
+            # must restrict itself to those.
+            [[ "$*" == *viewerDidAuthor* ]] || { echo "comments query must filter by viewerDidAuthor" >&2; exit 1; }
+            cat "${MOCK_COMMENTS_FILE:-/dev/null}";;
         *) echo "unhandled pr view: $*" >&2; exit 1;;
     esac
 elif [[ "$1 $2" == "pr comment" ]]; then
@@ -167,5 +171,20 @@ grep -q -- "--base" "$CALLS" && fail "D: base must NOT be edited"
 [[ "$(git -C "$ORIGIN" rev-parse child)" == "$CHILD_BEFORE" ]] || fail "D: child was pushed"
 ok "D: missing target detected, no branch mutation, label removed"
 
+# ---------------------------------------------------------------------------
+echo "### Scenario E: malformed state marker -> no mutation"
+setup_repo
+MOCK_LABELS="autorestack-needs-conflict-resolution"
+PR_BASE="parent"
+MOCK_COMMENTS_FILE="$WORK/comments.txt"
+{ echo "### conflict"; echo; echo '<!-- autorestack-state: base=parent target=main -->'; } > "$MOCK_COMMENTS_FILE"
+run_resume
+
+grep -q "remove-label autorestack-needs-conflict-resolution" "$CALLS" || fail "E: label not removed"
+grep -q "gh pr comment" "$CALLS" || fail "E: no explanatory comment posted"
+grep -q -- "--base" "$CALLS" && fail "E: base must NOT be edited"
+[[ "$(git -C "$ORIGIN" rev-parse child)" == "$CHILD_BEFORE" ]] || fail "E: child was pushed"
+ok "E: malformed marker handled, no branch mutation, label removed"
+
 echo
 echo "All conflict-resume tests passed 🎉 ($PASS scenarios)"
diff --git a/update-pr-stack.sh b/update-pr-stack.sh
index 504580b..2596fd8 100755
--- a/update-pr-stack.sh
+++ b/update-pr-stack.sh
@@ -39,13 +39,17 @@ format_state_marker() {
         "$STATE_MARKER_PREFIX" "$1" "$2" "$3"
 }
 
-# Echoes the most recent state-marker line found in our PR comments, or nothing.
-# A failed comments fetch aborts the run: treating it as "no marker" would make
-# the caller abandon the resume and drop the conflict label for good.
+# Echoes the most recent state-marker line found in PR comments, or nothing.
+# Only comments posted with our own token count (viewerDidAuthor): anyone can
+# comment a marker, and acting on a forged one would merge and push an
+# attacker-chosen commit. A failed comments fetch aborts the run: treating it
+# as "no marker" would make the caller abandon the resume and drop the
+# conflict label for good.
 read_state_marker() {
     local PR_NUMBER="$1"
     local BODIES
-    if ! BODIES=$(gh pr view "$PR_NUMBER" --json comments --jq '.comments[].body'); then
+    if ! BODIES=$(gh pr view "$PR_NUMBER" --json comments \
+            --jq '.comments[] | select(.viewerDidAuthor) | .body'); then
         echo "Error: could not read comments of PR #$PR_NUMBER" >&2
         exit 1
     fi
@@ -252,6 +256,12 @@ continue_after_resolution() {
     read -r OLD_BASE NEW_TARGET SQUASH_HASH < <(parse_state_marker "$MARKER")
     echo "Recorded state: base=$OLD_BASE target=$NEW_TARGET squash=$SQUASH_HASH"
 
+    if [[ -z "$OLD_BASE" || -z "$NEW_TARGET" || -z "$SQUASH_HASH" ]]; then
+        echo "⚠️ State marker on $PR_BRANCH is malformed; cannot resume safely. Removing the label."
+        abandon_resume "$PR_NUMBER" "ℹ️ autorestack found a malformed state marker on this PR, so it will not update the stack automatically. If this PR still needs its base updated, update its base manually."
+        return
+    fi
+
     # The PR was left based on the merged parent branch. If the payload shows a
     # different base, a human retargeted the PR; the recorded target is stale,
     # so step back before any mutation.