diff --git a/scripts/consistency_check.py b/scripts/consistency_check.py
index ab14107..6bf12e2 100644
--- a/scripts/consistency_check.py
+++ b/scripts/consistency_check.py
@@ -17,6 +17,7 @@ Checks:
   C-10  task-status-drift        WARN  Yes  Task status differs between file and DB
   C-11  task-unlinked            WARN  Yes  Task block has no state_hub_task_id
   C-12  orphan-db-task           WARN  No   DB task in workstream has no file backing
+  C-13  workstream-auto-complete WARN  Yes  All DB tasks done but workstream still active
 
 Usage:
     python scripts/consistency_check.py --repo SLUG [--fix] [--json] [--api-base URL]
@@ -535,6 +536,32 @@ def check_repo(api_base: str, repo_slug: str) -> ConsistencyReport:
                         fixable=False,
                     )
 
+        # C-13: all DB tasks done but workstream still active — worker forgot to close
+        db_status = ws.get("status", "")
+        if db_status == "active" and isinstance(db_tasks, list) and db_tasks:
+            non_terminal = [
+                t for t in db_tasks
+                if t.get("status") not in ("done", "cancelled")
+            ]
+            if not non_terminal:
+                report.add(
+                    severity="WARN", check_id="C-13",
+                    message=(
+                        f"All {len(db_tasks)} DB tasks for '{ws.get('slug')}' are "
+                        f"done/cancelled but workstream status is still 'active' — "
+                        f"worker likely forgot update_workstream_status()"
+                    ),
+                    file_path=fname,
+                    db_id=ws_id,
+                    db_value="active",
+                    fixable=True,
+                    _fix_context={
+                        "ws_id": ws_id,
+                        "field": "status",
+                        "value": "completed",
+                    },
+                )
+
     # C-07 / C-08: orphan DB workstreams (have repo_id=this_repo but no backing file)
     _check_orphan_db(api_base, repo_id, set(file_ws_ids.keys()), report)
 
@@ -588,7 +615,7 @@ def fix_repo(api_base: str, repo_slug: str) -> ConsistencyReport:
     for issue in fixable:
         ctx = issue._fix_context
         try:
-            if issue.check_id in ("C-04", "C-05"):
+            if issue.check_id in ("C-04", "C-05", "C-13"):
                 ws_id = ctx["ws_id"]
                 result = _api_patch(api_base, f"/workstreams/{ws_id}",
                                     {ctx["field"]: ctx["value"]})