diff --git a/slack_sdk/socket_mode/builtin/connection.py b/slack_sdk/socket_mode/builtin/connection.py
index 588f50497..f724ffaa0 100644
--- a/slack_sdk/socket_mode/builtin/connection.py
+++ b/slack_sdk/socket_mode/builtin/connection.py
@@ -249,7 +249,11 @@ def check_state(self) -> None:
         try:
             if self.sock is not None:
                 try:
-                    self.ping(f"{self.session_id}:{time.time()}")
+                    ping_time = time.time()
+                    self.ping(f"{self.session_id}:{ping_time}")
+                    # Seed on first ping so the stale check fires even if no pong ever arrives.
+                    if self.last_ping_pong_time is None:
+                        self.last_ping_pong_time = ping_time
                 except ssl.SSLZeroReturnError as e:
                     self.logger.info(
                         "Unable to send a ping message. Closing the connection..."
diff --git a/tests/slack_sdk/socket_mode/test_builtin.py b/tests/slack_sdk/socket_mode/test_builtin.py
index 6ba64c9a3..7ade10f7c 100644
--- a/tests/slack_sdk/socket_mode/test_builtin.py
+++ b/tests/slack_sdk/socket_mode/test_builtin.py
@@ -3,7 +3,7 @@
 import ssl
 import time
 import unittest
-from unittest.mock import patch, sentinel
+from unittest.mock import MagicMock, patch, sentinel
 from threading import Thread
 
 from slack_sdk import WebClient
@@ -126,6 +126,23 @@ def run():
 
         self.assertIsNotNone(conn)
 
+    def test_check_state_seeds_last_ping_pong_time_on_first_ping(self):
+        conn = Connection(url="wss://example.com", logger=self.logger)
+        conn.sock = MagicMock()
+        self.assertIsNone(conn.last_ping_pong_time)
+        with patch.object(conn, "ping"):
+            conn.check_state()
+        self.assertIsNotNone(conn.last_ping_pong_time)
+
+    def test_check_state_does_not_overwrite_existing_last_ping_pong_time(self):
+        conn = Connection(url="wss://example.com", logger=self.logger)
+        conn.sock = MagicMock()
+        existing_time = time.time() - 1
+        conn.last_ping_pong_time = existing_time
+        with patch.object(conn, "ping"):
+            conn.check_state()
+        self.assertEqual(conn.last_ping_pong_time, existing_time)
+
     # ----------------------------------
     # FrameHeader