diff --git a/library.json b/library.json
index e057f02d..b9673907 100644
--- a/library.json
+++ b/library.json
@@ -6,7 +6,7 @@
         "type": "git",
         "url": "https://github.com/knolleary/pubsubclient.git"
     },
-    "version": "2.5",
+    "version": "2.6",
     "exclude": "tests",
     "examples": "examples/*/*.ino",
     "frameworks": "arduino",
diff --git a/library.properties b/library.properties
index fc673cd9..3ceeda81 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=PubSubClient
-version=2.5
+version=2.6
 author=Nick O'Leary <nick.oleary@gmail.com>
 maintainer=Nick O'Leary <nick.oleary@gmail.com>
 sentence=A client library for MQTT messaging.
diff --git a/src/PubSubClient.h b/src/PubSubClient.h
index f9792c00..be4bd674 100755
--- a/src/PubSubClient.h
+++ b/src/PubSubClient.h
@@ -75,9 +75,9 @@
 
 #ifdef ESP8266
 #include <functional>
-#define MQTT_CALLBACK_SIGNATURE std::function<void(char*, uint8_t*, uint32_t)> callback
+#define MQTT_CALLBACK_SIGNATURE std::function<void(char*, uint8_t*, unsigned int)> callback
 #else
-#define MQTT_CALLBACK_SIGNATURE void (*callback)(char*, uint8_t*, uint32_t)
+#define MQTT_CALLBACK_SIGNATURE void (*callback)(char*, uint8_t*, unsigned int)
 #endif
 
 class PubSubClient {