diff --git a/lib/index.ts b/lib/index.ts
index bf51f80..f9266b9 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -82,14 +82,14 @@ export class Adapter extends EventEmitter {
     this._del(room, id);
   }
 
-  private _del(room, id) {
-    if (this.rooms.has(room)) {
-      const deleted = this.rooms.get(room).delete(id);
+  private _del(room: Room, id: SocketId) {
+    const _room = this.rooms.get(room);
+    if (_room != null) {
+      const deleted = _room.delete(id);
       if (deleted) {
         this.emit("leave-room", room, id);
       }
-      if (this.rooms.get(room).size === 0) {
-        this.rooms.delete(room);
+      if (_room.size === 0 && this.rooms.delete(room)) {
         this.emit("delete-room", room);
       }
     }
diff --git a/test/index.js b/test/index.js
index ce8b25e..f4729c4 100644
--- a/test/index.js
+++ b/test/index.js
@@ -230,6 +230,16 @@ describe("socket.io-adapter", () => {
       adapter.del("s1", "r1");
     });
 
+    it("should not throw when calling del twice", done => {
+      const adapter = new Adapter({ server: { encoder: null } });
+      adapter.on("leave-room", (room, sid) => {
+        adapter.del("s1", "r1");
+        process.nextTick(done);
+      });
+      adapter.addAll("s1", new Set(["r1"]));
+      adapter.del("s1", "r1");
+    });
+
     it("should emit a 'leave-room' event with delAll method", done => {
       const adapter = new Adapter({ server: { encoder: null } });
       adapter.on("leave-room", (room, sid) => {