diff --git a/aiida/engine/processes/process.py b/aiida/engine/processes/process.py
index 069b84ae26..bbb2dcdf40 100644
--- a/aiida/engine/processes/process.py
+++ b/aiida/engine/processes/process.py
@@ -903,6 +903,8 @@ def exposed_outputs(
         for port_namespace in self._get_namespace_list(namespace=namespace, agglomerate=agglomerate):
             # only the top-level key is stored in _exposed_outputs
             for top_name in top_namespace_map:
+                if namespace is not None and namespace not in self.spec()._exposed_outputs:  # pylint: disable=protected-access
+                    raise KeyError(f'the namespace `{namespace}` is not an exposed namespace.')
                 if top_name in self.spec()._exposed_outputs[port_namespace][process_class]:  # pylint: disable=protected-access
                     output_key_map[top_name] = port_namespace
 
diff --git a/tests/engine/test_process.py b/tests/engine/test_process.py
index 738607f75f..691e3a3d96 100644
--- a/tests/engine/test_process.py
+++ b/tests/engine/test_process.py
@@ -393,3 +393,46 @@ def define(cls, spec):
             'output': node_output,
         })
         self.assertEqual(exposed_outputs, expected)
+
+    def test_exposed_outputs_non_existing_namespace(self):
+        """Test the ``Process.exposed_outputs`` method for non-existing namespace."""
+        from aiida.common.links import LinkType
+        from aiida.engine.utils import instantiate_process
+        from aiida.manage.manager import get_manager
+
+        runner = get_manager().get_runner()
+
+        class ChildProcess(Process):
+            """Dummy process with normal output and output namespace."""
+
+            _node_class = orm.WorkflowNode
+
+            @classmethod
+            def define(cls, spec):
+                super(ChildProcess, cls).define(spec)
+                spec.input('input', valid_type=orm.Int)
+                spec.output('output', valid_type=orm.Int)
+                spec.output('name.space', valid_type=orm.Int)
+
+        class ParentProcess(Process):
+            """Dummy process that exposes the outputs of ``ChildProcess``."""
+
+            _node_class = orm.WorkflowNode
+
+            @classmethod
+            def define(cls, spec):
+                super(ParentProcess, cls).define(spec)
+                spec.input('input', valid_type=orm.Int)
+                spec.expose_outputs(ChildProcess, namespace='child')
+
+        node_child = orm.WorkflowNode().store()
+        node_output = orm.Int(1).store()
+        node_output.add_incoming(node_child, link_label='output', link_type=LinkType.RETURN)
+        node_name_space = orm.Int(1).store()
+        node_name_space.add_incoming(node_child, link_label='name__space', link_type=LinkType.RETURN)
+
+        process = instantiate_process(runner, ParentProcess, input=orm.Int(1))
+
+        # If the ``namespace`` does not exist, for example because it is slightly misspelled, a ``KeyError`` is raised
+        with self.assertRaises(KeyError):
+            process.exposed_outputs(node_child, ChildProcess, namespace='cildh')