diff --git a/Adafruit_MQTT.cpp b/Adafruit_MQTT.cpp
index 87fea10..443fc69 100644
--- a/Adafruit_MQTT.cpp
+++ b/Adafruit_MQTT.cpp
@@ -234,6 +234,7 @@ Adafruit_MQTT_Subscribe *Adafruit_MQTT::readSubscription(int16_t timeout) {
   }
   // extract out just the data, into the subscription object itself
   memcpy(subscriptions[i]->lastread, buffer+4+topiclen, datalen);
+  subscriptions[i]->datalen = datalen;
   DEBUG_PRINT(F("Data len: ")); DEBUG_PRINTLN(datalen);
   DEBUG_PRINT(F("Data: ")); DEBUG_PRINTLN((char *)subscriptions[i]->lastread);
 
diff --git a/Adafruit_MQTT.h b/Adafruit_MQTT.h
index 82e5bc1..0fe5ed4 100644
--- a/Adafruit_MQTT.h
+++ b/Adafruit_MQTT.h
@@ -203,6 +203,9 @@ class Adafruit_MQTT_Subscribe {
   uint8_t qos;
 
   uint8_t lastread[SUBSCRIPTIONDATALEN];
+  // Number valid bytes in lastread. Limited to SUBSCRIPTIONDATALEN-1 to
+  // ensure nul terminating lastread.
+  uint8_t datalen;
  private:
   Adafruit_MQTT *mqtt;
 };