diff --git a/src/c3nav/mapdata/fields.py b/src/c3nav/mapdata/fields.py
index d1cbd30c..7985aa96 100644
--- a/src/c3nav/mapdata/fields.py
+++ b/src/c3nav/mapdata/fields.py
@@ -5,6 +5,7 @@ import typing
 from django.core.exceptions import ValidationError
 from django.core.validators import RegexValidator
 from django.db import models
+from django.utils.functional import cached_property
 from django.utils.translation import ugettext_lazy as _
 from shapely import validation
 from shapely.geometry import LineString, MultiPolygon, Point, Polygon, mapping, shape
@@ -68,15 +69,19 @@ class GeometryField(models.TextField):
         self._validate_geomtype(geometry)
         return geometry
 
+    @cached_property
+    def classes(self):
+        return {
+            'polygon': (Polygon, ),
+            'multipolygon': (Polygon, MultiPolygon),
+            'linestring': (LineString, ),
+            'point': (Point, )
+        }[self.geomtype]
+
     def _validate_geomtype(self, value, exception: typing.Type[Exception]=ValidationError):
-        if self.geomtype == 'polygon' and not isinstance(value, Polygon):
-            raise exception('Expected Polygon instance, got %s instead.' % repr(value))
-        if self.geomtype == 'multipolygon' and not isinstance(value, (Polygon, MultiPolygon)):
-            raise exception('Expected Polygon or MultiPolygon instance, got %s instead.' % repr(value))
-        elif self.geomtype == 'linestring' and not isinstance(value, LineString):
-            raise exception('Expected LineString instance, got %s instead.' % repr(value))
-        elif self.geomtype == 'point' and not isinstance(value, Point):
-            raise exception('Expected Point instance, got %s instead.' % repr(value))
+        if not isinstance(value, self.classes):
+            raise exception('Expected %s instance, got %s instead.' % (' or '.join(c.__name__ for c in self.classes),
+                                                                       repr(value)))
 
     def get_final_value(self, value, as_json=False):
         json_value = format_geojson(mapping(value))