diff --git a/scripts/branch.sh b/scripts/branch.sh
index 6352c3b..61dd5c4 100644
--- a/scripts/branch.sh
+++ b/scripts/branch.sh
@@ -448,7 +448,7 @@ function branch_script {
                             "$main_branch"|"$current_branch"|master|main|develop) continue ;;
                         esac
                         merged_to_delete+=("$_mb")
-                    done < <(git branch --merged --format='%(refname:short)')
+                    done < <(git branch --merged HEAD --format='%(refname:short)')
 
                     for branch_to_delete in "${merged_to_delete[@]}"; do
                         delete_output=$(git branch -d "$branch_to_delete" 2>&1)
diff --git a/tests/test_branch_operations.bats b/tests/test_branch_operations.bats
index 351c769..033966d 100644
--- a/tests/test_branch_operations.bats
+++ b/tests/test_branch_operations.bats
@@ -99,6 +99,24 @@ teardown() {
     [ "$status" -ne 0 ]
 }
 
+@test "branch deletion: merged-branch listing used by gitb branch delete works" {
+    create_test_branch "feature/merged"
+    make_test_commit "feature.txt" "Feature work"
+    git checkout main
+    git merge feature/merged --no-edit
+
+    run git branch --merged HEAD --format='%(refname:short)'
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"feature/merged"* ]]
+}
+
+@test "branch deletion: --merged is never followed directly by another flag" {
+    # `--merged`/`--no-merged` take an optional commit, so git parses a
+    # following `--format=...` as that commit: "malformed object name".
+    run grep -rnE -- '--(no-)?merged +-' "${GITBASHER_ROOT}/scripts"
+    [ "$status" -ne 0 ]
+}
+
 # ===== Remote branch tests =====
 
 @test "remote branches: can fetch from remote" {