diff --git a/libraries/ESP8266WiFi/src/include/ClientContext.h b/libraries/ESP8266WiFi/src/include/ClientContext.h
index b2628f8032..43e9040a48 100644
--- a/libraries/ESP8266WiFi/src/include/ClientContext.h
+++ b/libraries/ESP8266WiFi/src/include/ClientContext.h
@@ -131,6 +131,11 @@ class ClientContext
         _op_start_time = millis();
         // This delay will be interrupted by esp_schedule in the connect callback
         delay(_timeout_ms);
+        // WiFi may have vanished during the delay (#4078)
+        if (!this || !_pcb) {
+            DEBUGV(":vnsh\r\n");
+            return 0;
+        }
         _connect_pending = 0;
         if (state() != ESTABLISHED) {
             abort();