diff --git a/src/cloud-sql-instance.ts b/src/cloud-sql-instance.ts
index 23b1506b..3dc2e329 100644
--- a/src/cloud-sql-instance.ts
+++ b/src/cloud-sql-instance.ts
@@ -364,12 +364,14 @@ export class CloudSQLInstance {
       this.checkDomainID = null;
     }
     for (const socket of this.sockets) {
-      socket.destroy(
-        new CloudSQLConnectorError({
-          code: 'ERRCLOSED',
-          message: 'The connector was closed.',
-        })
-      );
+      if (typeof socket.destroy === 'function') {
+        socket.destroy(
+          new CloudSQLConnectorError({
+            code: 'ERRCLOSED',
+            message: 'The connector was closed.',
+          })
+        );
+      }
     }
   }
 
@@ -391,15 +393,15 @@ export class CloudSQLInstance {
     }
   }
   addSocket(socket: DestroyableSocket) {
-    if (!this.instanceInfo.domainName) {
-      // This was not connected by domain name. Ignore all sockets.
-      return;
-    }
-
-    // Add the socket to the list
+    // Track all active sockets created by this instance so they can
+    // be forcefully cleaned up during a domain change or when
+    // the connector is explicitly closed.
     this.sockets.add(socket);
-    // When the socket is closed, remove it.
-    socket.once('closed', () => {
+
+    // When the socket is closed by the driver or peer, remove it
+    // from our tracking set to prevent reference memory leaks.
+    // Note: Node.js TLSSocket/Socket emits 'close', not 'closed'.
+    socket.once('close', () => {
       this.sockets.delete(socket);
     });
   }
diff --git a/src/connector.ts b/src/connector.ts
index 37848473..111ad141 100644
--- a/src/connector.ts
+++ b/src/connector.ts
@@ -358,8 +358,17 @@ export class Connector {
   //
   // Also clear up any local proxy servers and socket connections.
   close(): void {
-    for (const instance of this.instances.values()) {
-      instance.promise.then(inst => inst.close());
+    for (const entry of this.instances.values()) {
+      if (entry.isResolved() && entry.instance) {
+        // If the instance is already resolved, close it synchronously.
+        // This prevents a race condition with immediate connection pool close
+        // (e.g., pool.end()) where asynchronous microtasks would execute too late.
+        entry.instance.close();
+      } else {
+        // Otherwise, close the instance asynchronously once its initial
+        // refresh has finished.
+        entry.promise.then(inst => inst.close()).catch(() => {});
+      }
     }
     for (const server of this.localProxies) {
       server.close();