diff --git a/django/db/backends/sqlite3/_functions.py b/django/db/backends/sqlite3/_functions.py
index a699db0591..f1fcd6e3a5 100644
--- a/django/db/backends/sqlite3/_functions.py
+++ b/django/db/backends/sqlite3/_functions.py
@@ -135,6 +135,7 @@ def _sqlite_date_trunc(lookup_type, dt, tzname, conn_tzname):
         return f'{dt.year:04d}-{dt.month:02d}-{dt.day:02d}'
     elif lookup_type == 'day':
         return f'{dt.year:04d}-{dt.month:02d}-{dt.day:02d}'
+    raise ValueError(f'Unsupported lookup type: {lookup_type!r}')
 
 
 def _sqlite_time_trunc(lookup_type, dt, tzname, conn_tzname):
@@ -154,6 +155,7 @@ def _sqlite_time_trunc(lookup_type, dt, tzname, conn_tzname):
         return f'{dt.hour:02d}:{dt.minute:02d}:00'
     elif lookup_type == 'second':
         return f'{dt.hour:02d}:{dt.minute:02d}:{dt.second:02d}'
+    raise ValueError(f'Unsupported lookup type: {lookup_type!r}')
 
 
 def _sqlite_datetime_cast_date(dt, tzname, conn_tzname):
@@ -210,6 +212,7 @@ def _sqlite_datetime_trunc(lookup_type, dt, tzname, conn_tzname):
         return f'{dt.year:04d}-{dt.month:02d}-{dt.day:02d} {dt.hour:02d}:{dt.minute:02d}:00'
     elif lookup_type == 'second':
         return f'{dt.year:04d}-{dt.month:02d}-{dt.day:02d} {dt.hour:02d}:{dt.minute:02d}:{dt.second:02d}'
+    raise ValueError(f'Unsupported lookup type: {lookup_type!r}')
 
 
 def _sqlite_time_extract(lookup_type, dt):
diff --git a/tests/backends/sqlite/test_functions.py b/tests/backends/sqlite/test_functions.py
new file mode 100644
index 0000000000..0659717799
--- /dev/null
+++ b/tests/backends/sqlite/test_functions.py
@@ -0,0 +1,21 @@
+from django.db.backends.sqlite3._functions import (
+    _sqlite_date_trunc, _sqlite_datetime_trunc, _sqlite_time_trunc,
+)
+from django.test import SimpleTestCase
+
+
+class FunctionTests(SimpleTestCase):
+    def test_sqlite_date_trunc(self):
+        msg = "Unsupported lookup type: 'unknown-lookup'"
+        with self.assertRaisesMessage(ValueError, msg):
+            _sqlite_date_trunc('unknown-lookup', '2005-08-11', None, None)
+
+    def test_sqlite_datetime_trunc(self):
+        msg = "Unsupported lookup type: 'unknown-lookup'"
+        with self.assertRaisesMessage(ValueError, msg):
+            _sqlite_datetime_trunc('unknown-lookup', '2005-08-11 1:00:00', None, None)
+
+    def test_sqlite_time_trunc(self):
+        msg = "Unsupported lookup type: 'unknown-lookup'"
+        with self.assertRaisesMessage(ValueError, msg):
+            _sqlite_time_trunc('unknown-lookup', '2005-08-11 1:00:00', None, None)