diff --git a/src/_pytest/reports.py b/src/_pytest/reports.py
index cd7a0b57f..679d72c9d 100644
--- a/src/_pytest/reports.py
+++ b/src/_pytest/reports.py
@@ -422,4 +422,6 @@ def pytest_report_unserialize(data):
             return TestReport._from_json(data)
         elif data["_report_type"] == "CollectReport":
             return CollectReport._from_json(data)
-        assert "Unknown report_type unserialize data: {}".format(data["_report_type"])
+        assert False, "Unknown report_type unserialize data: {}".format(
+            data["_report_type"]
+        )
diff --git a/testing/test_reports.py b/testing/test_reports.py
index 879a9098d..22d5fce34 100644
--- a/testing/test_reports.py
+++ b/testing/test_reports.py
@@ -249,7 +249,6 @@ class TestHooks:
     def test_test_report(self, testdir, pytestconfig):
         testdir.makepyfile(
             """
-            import os
             def test_a(): assert False
             def test_b(): pass
         """
@@ -272,7 +271,6 @@ class TestHooks:
     def test_collect_report(self, testdir, pytestconfig):
         testdir.makepyfile(
             """
-            import os
             def test_a(): assert False
             def test_b(): pass
         """
@@ -291,3 +289,25 @@ class TestHooks:
             assert new_rep.nodeid == rep.nodeid
             assert new_rep.when == "collect"
             assert new_rep.outcome == rep.outcome
+
+    @pytest.mark.parametrize(
+        "hook_name", ["pytest_runtest_logreport", "pytest_collectreport"]
+    )
+    def test_invalid_report_types(self, testdir, pytestconfig, hook_name):
+        testdir.makepyfile(
+            """
+            def test_a(): pass
+            """
+        )
+        reprec = testdir.inline_run()
+        reports = reprec.getreports(hook_name)
+        assert reports
+        rep = reports[0]
+        data = pytestconfig.hook.pytest_report_serialize(
+            config=pytestconfig, report=rep
+        )
+        data["_report_type"] = "Unknown"
+        with pytest.raises(AssertionError):
+            _ = pytestconfig.hook.pytest_report_unserialize(
+                config=pytestconfig, data=data
+            )