diff --git a/deploy.prod.sh b/deploy.prod.sh
index d721b2d..482f426 100755
--- a/deploy.prod.sh
+++ b/deploy.prod.sh
@@ -9,12 +9,12 @@ set -Eeuo pipefail
 PROJECT_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 cd "$PROJECT_ROOT"
 
-BRANCH="${1:-main}"
+BRANCH_INPUT="${1:-}"
 REMOTE="${2:-origin}"
 
 echo "==> [prod] Project: $PROJECT_ROOT"
 echo "==> [prod] Remote:  $REMOTE"
-echo "==> [prod] Branch:  $BRANCH"
+echo "==> [prod] Branch:  ${BRANCH_INPUT:-<auto>}"
 
 if [[ ! -d ".git" ]]; then
   echo "Error: current directory is not a git repository."
@@ -29,6 +29,38 @@ fi
 echo "==> [prod] Fetching latest code"
 git fetch "$REMOTE" --prune
 
+resolve_default_branch() {
+  local remote="$1"
+  local head_ref
+  head_ref="$(git symbolic-ref -q --short "refs/remotes/$remote/HEAD" 2>/dev/null || true)"
+  if [[ -n "$head_ref" ]]; then
+    echo "${head_ref#${remote}/}"
+    return 0
+  fi
+  head_ref="$(git remote show "$remote" 2>/dev/null | awk '/HEAD branch/ {print $NF; exit}')"
+  if [[ -n "$head_ref" ]]; then
+    echo "$head_ref"
+    return 0
+  fi
+  return 1
+}
+
+if [[ -n "$BRANCH_INPUT" ]]; then
+  BRANCH="$BRANCH_INPUT"
+else
+  BRANCH="$(resolve_default_branch "$REMOTE" || true)"
+  if [[ -z "$BRANCH" ]]; then
+    BRANCH="$(git rev-parse --abbrev-ref HEAD 2>/dev/null || true)"
+  fi
+  if [[ -z "$BRANCH" || "$BRANCH" == "HEAD" ]]; then
+    echo "Error: could not determine deploy branch. Please pass one explicitly:"
+    echo "  sh deploy.prod.sh <branch> [remote]"
+    exit 1
+  fi
+fi
+
+echo "==> [prod] Using branch: $BRANCH"
+
 if ! git show-ref --verify --quiet "refs/remotes/$REMOTE/$BRANCH"; then
   echo "Error: remote branch '$REMOTE/$BRANCH' not found."
   exit 1