diff --git a/spinach/engine.py b/spinach/engine.py
index f1ac7b9..f37490f 100644
--- a/spinach/engine.py
+++ b/spinach/engine.py
@@ -10,7 +10,7 @@
 from .brokers.base import Broker
 from .const import DEFAULT_QUEUE, DEFAULT_NAMESPACE
 from .worker import Workers
-from . import signals
+from . import signals, exc
 
 
 logger = getLogger(__name__)
@@ -55,13 +55,14 @@ def attach_tasks(self, tasks: Tasks):
         tasks._spin = self
 
     def _get_task(self, name) -> Task:
-        try:
-            return self._tasks[name]
-        except KeyError:
-            raise ValueError(
-                'Unknown task "{}". Known tasks: {}'
-                .format(name, list(self._tasks.keys()))
-            )
+        task = self._tasks.get(name)
+        if task is not None:
+            return task
+
+        raise exc.UnknownTask(
+            'Unknown task "{}", known tasks: {}'
+            .format(name, list(self._tasks.keys()))
+        )
 
     def execute(self, task_name: str, *args, **kwargs):
         return self._get_task(task_name).func(*args, **kwargs)
@@ -102,8 +103,12 @@ def _arbiter_func(self):
                 job = self._broker.get_job_from_queue(self._working_queue)
 
                 while job:
-                    job.task_func = self._get_task(job.task_name).func
-                    self._workers.submit_job(job)
+                    try:
+                        job.task_func = self._get_task(job.task_name).func
+                    except exc.UnknownTask as err:
+                        self._job_finished_callback(job, 0.0, err)
+                    else:
+                        self._workers.submit_job(job)
 
                     if self._workers.can_accept_job():
                         job = self._broker.get_job_from_queue(
diff --git a/spinach/exc.py b/spinach/exc.py
new file mode 100644
index 0000000..f274507
--- /dev/null
+++ b/spinach/exc.py
@@ -0,0 +1,6 @@
+class SpinachError(Exception):
+    """Base class for other Spinach exceptions."""
+
+
+class UnknownTask(SpinachError):
+    """Task name is not registered with the Engine."""
diff --git a/tests/test_engine.py b/tests/test_engine.py
index b81b823..08fb33c 100644
--- a/tests/test_engine.py
+++ b/tests/test_engine.py
@@ -1,9 +1,12 @@
 from datetime import datetime, timezone
+from unittest.mock import patch
+import time
 
 import pytest
 
 from spinach import Engine, MemoryBroker, RetryException
 from spinach.job import Job, JobStatus
+from spinach.exc import UnknownTask
 
 
 @pytest.fixture
@@ -43,3 +46,8 @@ def test_job_finished_callback(spin):
     job.max_retries = 0
     spin._job_finished_callback(job, 1.0, RetryException('Must retry', at=now))
     assert job.status is JobStatus.FAILED
+
+
+def test_schedule_unknown_task(spin):
+    with pytest.raises(UnknownTask):
+        spin.schedule('foo_task')