diff --git a/libraries/Wire/Wire.cpp b/libraries/Wire/Wire.cpp
index 906b22eed..7e8689499 100644
--- a/libraries/Wire/Wire.cpp
+++ b/libraries/Wire/Wire.cpp
@@ -212,7 +212,7 @@ void TwoWire::flush(void){
   txBufferLength = 0;
 }
 
-void TwoWire::onReceiveService(uint8_t* inBytes, int numBytes)
+void TwoWire::onReceiveService(uint8_t* inBytes, size_t numBytes)
 {
   // don't bother if user hasn't registered a callback
   if (!user_onReceive) {
diff --git a/libraries/Wire/Wire.h b/libraries/Wire/Wire.h
index e14b90a52..e697bcca0 100644
--- a/libraries/Wire/Wire.h
+++ b/libraries/Wire/Wire.h
@@ -47,7 +47,7 @@ class TwoWire : public Stream
     static void (*user_onRequest)(void);
     static void (*user_onReceive)(int);
     static void onRequestService(void);
-    static void onReceiveService(uint8_t*, int);
+    static void onReceiveService(uint8_t*, size_t);
   public:
     TwoWire();
     void begin(int sda, int scl);