diff --git a/src/ert/scheduler/job.py b/src/ert/scheduler/job.py
index c48f576dd67..f524a8971b4 100644
--- a/src/ert/scheduler/job.py
+++ b/src/ert/scheduler/job.py
@@ -147,7 +147,8 @@ async def run(self, sem: asyncio.BoundedSemaphore, max_submit: int = 1) -> None:
             if self.returncode.result() == 0:
                 if self._scheduler._manifest_queue is not None:
                     await self._verify_checksum()
-                await self._handle_finished_forward_model()
+                async with self._scheduler._forward_model_ok_lock:
+                    await self._handle_finished_forward_model()
                 break
 
             if attempt < max_submit - 1:
diff --git a/src/ert/scheduler/scheduler.py b/src/ert/scheduler/scheduler.py
index 71ac4213c15..9982a7d935f 100644
--- a/src/ert/scheduler/scheduler.py
+++ b/src/ert/scheduler/scheduler.py
@@ -106,6 +106,10 @@ def __init__(
         self._completed_jobs_num: int = 0
         self.completed_jobs: asyncio.Queue[int] = asyncio.Queue()
 
+        # this lock is to assure that no more than 1 task
+        # does internalization at a time
+        self._forward_model_ok_lock: asyncio.Lock = asyncio.Lock()
+
         self._cancelled = False
         if max_submit < 0:
             raise ValueError(