diff --git a/hal/api/CAN.h b/hal/api/CAN.h
index 65221ccdec..241cd4c822 100644
--- a/hal/api/CAN.h
+++ b/hal/api/CAN.h
@@ -218,8 +218,20 @@ public:
     *  @param method pointer to the member function to be called
     *  @param event Which CAN interrupt to attach the member function to (CAN::RxIrq for message received, TxIrq for transmitted or aborted, EwIrq for error warning, DoIrq for data overrun, WuIrq for wake-up, EpIrq for error passive, AlIrq for arbitration lost, BeIrq for bus error)
     */
-   template<typename T>
-   void attach(T* obj, void (T::*method)(void), IrqType type=RxIrq) {
+    template<typename T>
+    void attach(T* obj, void (T::*method)(), IrqType type=RxIrq) {
+        attach(Callback<void()>(obj, method), type);
+    }
+
+   /** Attach a member function to call whenever a CAN frame received interrupt
+    *  is generated.
+    *
+    *  @param obj pointer to the object to call the member function on
+    *  @param method pointer to the member function to be called
+    *  @param event Which CAN interrupt to attach the member function to (CAN::RxIrq for message received, TxIrq for transmitted or aborted, EwIrq for error warning, DoIrq for data overrun, WuIrq for wake-up, EpIrq for error passive, AlIrq for arbitration lost, BeIrq for bus error)
+    */
+    template<typename T>
+    void attach(T* obj, void (*method)(T*), IrqType type=RxIrq) {
         attach(Callback<void()>(obj, method), type);
     }
 
diff --git a/hal/api/Callback.h b/hal/api/Callback.h
index d7b4d12ec8..b90baf91af 100644
--- a/hal/api/Callback.h
+++ b/hal/api/Callback.h
@@ -106,6 +106,9 @@ public:
     /** Call the attached function
      */
     R call(A0 a0, A1 a1, A2 a2, A3 a3, A4 a4) {
+        if (!_thunk) {
+            return (R)0;
+        }
         return _thunk(_obj, &_func, a0, a1, a2, a3, a4);
     }
 
@@ -244,6 +247,9 @@ public:
     /** Call the attached function
      */
     R call(A0 a0, A1 a1, A2 a2, A3 a3) {
+        if (!_thunk) {
+            return (R)0;
+        }
         return _thunk(_obj, &_func, a0, a1, a2, a3);
     }
 
@@ -382,6 +388,9 @@ public:
     /** Call the attached function
      */
     R call(A0 a0, A1 a1, A2 a2) {
+        if (!_thunk) {
+            return (R)0;
+        }
         return _thunk(_obj, &_func, a0, a1, a2);
     }
 
@@ -520,6 +529,9 @@ public:
     /** Call the attached function
      */
     R call(A0 a0, A1 a1) {
+        if (!_thunk) {
+            return (R)0;
+        }
         return _thunk(_obj, &_func, a0, a1);
     }
 
@@ -658,6 +670,9 @@ public:
     /** Call the attached function
      */
     R call(A0 a0) {
+        if (!_thunk) {
+            return (R)0;
+        }
         return _thunk(_obj, &_func, a0);
     }
 
@@ -796,7 +811,7 @@ public:
     /** Call the attached function
      */
     R call() {
-        if (NULL == _thunk) {
+        if (!_thunk) {
             return (R)0;
         }
         return _thunk(_obj, &_func);
diff --git a/hal/api/SerialBase.h b/hal/api/SerialBase.h
index e9387f48ac..ed2e744790 100644
--- a/hal/api/SerialBase.h
+++ b/hal/api/SerialBase.h
@@ -100,8 +100,19 @@ public:
      *  @param method pointer to the member function to be called
      *  @param type Which serial interrupt to attach the member function to (Seriall::RxIrq for receive, TxIrq for transmit buffer empty)
      */
-    template<typename T, typename M>
-    void attach(T *obj, M method, IrqType type=RxIrq) {
+    template<typename T>
+    void attach(T *obj, void (T::*method)(), IrqType type=RxIrq) {
+        attach(Callback<void()>(obj, method), type);
+    }
+
+    /** Attach a member function to call whenever a serial interrupt is generated
+     *
+     *  @param obj pointer to the object to call the member function on
+     *  @param method pointer to the member function to be called
+     *  @param type Which serial interrupt to attach the member function to (Seriall::RxIrq for receive, TxIrq for transmit buffer empty)
+     */
+    template<typename T>
+    void attach(T *obj, void (*method)(T*), IrqType type=RxIrq) {
         attach(Callback<void()>(obj, method), type);
     }
 
diff --git a/net/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedSerial.h b/net/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedSerial.h
index 5c58928e72..07bcb9b245 100644
--- a/net/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedSerial.h
+++ b/net/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedSerial.h
@@ -149,8 +149,18 @@ public:
      *  @param method pointer to the member function to call
      *  @param type Which serial interrupt to attach the member function to (Serial::RxIrq for receive, TxIrq for transmit buffer empty)
      */
-    template <typename T, typename M>
-    void attach(T *obj, M method, IrqType type=RxIrq) {
+    template <typename T>
+    void attach(T *obj, void (T::*method)(), IrqType type=RxIrq) {
+        attach(Callback<void()>(obj, method), type);
+    }
+
+    /** Attach a member function to call whenever a serial interrupt is generated
+     *  @param obj pointer to the object to call the member function on
+     *  @param method pointer to the member function to call
+     *  @param type Which serial interrupt to attach the member function to (Serial::RxIrq for receive, TxIrq for transmit buffer empty)
+     */
+    template <typename T>
+    void attach(T *obj, void (*method)(T*), IrqType type=RxIrq) {
         attach(Callback<void()>(obj, method), type);
     }
 };