diff --git a/Adafruit_MQTT.cpp b/Adafruit_MQTT.cpp
index 1da9be2..85f91d8 100644
--- a/Adafruit_MQTT.cpp
+++ b/Adafruit_MQTT.cpp
@@ -239,6 +239,9 @@ void Adafruit_MQTT::processSubscriptionPacket(Adafruit_MQTT_Subscribe *sub) {
   } else if (sub->callback_io != NULL) {
     // execute callback in io mode
     ((sub->io_mqtt)->*(sub->callback_io))((char *)sub->lastread, sub->datalen);
+  } else {
+    DEBUG_PRINTLN("ERROR: Subscription packet did not have an associated callback");
+    return;
   }
   // mark subscription message as "read""
   sub->new_message = false;
diff --git a/library.properties b/library.properties
index 5231595..f2aca1f 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=Adafruit MQTT Library
-version=2.4.4
+version=2.5.0
 author=Adafruit
 maintainer=Adafruit <info@adafruit.com>
 sentence=MQTT library that supports the FONA, ESP8266, ESP32, Yun, and generic Arduino Client hardware.