diff --git a/roomserver/internal/helpers/sanity.go b/roomserver/internal/helpers/sanity.go
new file mode 100644
index 000000000..32fe47204
--- /dev/null
+++ b/roomserver/internal/helpers/sanity.go
@@ -0,0 +1,28 @@
+package helpers
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// SanityCheckEvent looks for any obvious problems with the event before
+// we bother to continue processing it any further.
+func SanityCheckEvent(event *gomatrixserverlib.Event) error {
+	switch event.Type() {
+	case gomatrixserverlib.MRoomCreate:
+		var content gomatrixserverlib.CreateContent
+		if err := json.Unmarshal(event.Content(), &content); err != nil {
+			return fmt.Errorf("Failed to unmarshal content of create event %q", event.EventID())
+		}
+
+		// Check that the room version is supported.
+		if content.RoomVersion != nil {
+			if _, err := content.RoomVersion.EventFormat(); err != nil {
+				return fmt.Errorf("Room version %q is unsupported in create event %q", *content.RoomVersion, event.EventID())
+			}
+		}
+	}
+	return nil
+}
diff --git a/roomserver/internal/input/input_events.go b/roomserver/internal/input/input_events.go
index f953a9259..394bb58ad 100644
--- a/roomserver/internal/input/input_events.go
+++ b/roomserver/internal/input/input_events.go
@@ -44,6 +44,17 @@ func (r *Inputer) processRoomEvent(
 	headered := input.Event
 	event := headered.Unwrap()
 
+	// Run sanity checks against the event. This will catch any really
+	// obvious problems.
+	if err = helpers.SanityCheckEvent(&event); err != nil {
+		logrus.WithFields(logrus.Fields{
+			"event_id": event.EventID(),
+			"type":     event.Type(),
+			"room":     event.RoomID(),
+		}).WithError(err).Info("Event failed sanity-checks")
+		return
+	}
+
 	// Check that the event passes authentication checks and work out
 	// the numeric IDs for the auth events.
 	isRejected := false