diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index abed6b5e6..2ceac19ad 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 from synapse.util.frozenutils import freeze
+from synapse.util.caches import intern_string
 
 
 # Whether we should use frozen_dict in FrozenEvent. Using frozen_dicts prevents
@@ -140,6 +141,12 @@ class FrozenEvent(EventBase):
 
         unsigned = dict(event_dict.pop("unsigned", {}))
 
+        # We intern these strings because they turn up a lot (especially when
+        # caching).
+        event_dict["type"] = intern_string(event_dict["type"])
+        if "state_key" in event_dict:
+            event_dict["state_key"] = intern_string(event_dict["state_key"])
+
         if USE_FROZEN_DICTS:
             frozen_dict = freeze(event_dict)
         else: