diff --git a/libraries/AP_Param/AP_Param.cpp b/libraries/AP_Param/AP_Param.cpp
index 996960a0b5..95814d5672 100644
--- a/libraries/AP_Param/AP_Param.cpp
+++ b/libraries/AP_Param/AP_Param.cpp
@@ -2078,7 +2078,7 @@ void AP_Param::convert_class(uint16_t param_key, void *object_pointer,
  convert width of a parameter, allowing update to wider scalar values
  without changing the parameter indexes
 */
-bool AP_Param::convert_parameter_width(ap_var_type old_ptype, float scale_factor)
+bool AP_Param::_convert_parameter_width(ap_var_type old_ptype, float scale_factor, bool bitmask)
 {
     if (configured_in_storage()) {
         // already converted or set by the user
@@ -2122,10 +2122,46 @@ bool AP_Param::convert_parameter_width(ap_var_type old_ptype, float scale_factor
     
     AP_Param *old_ap = (AP_Param *)&old_value[0];
 
-    // going via float is safe as the only time we would be converting
-    // from AP_Int32 is when converting to float
-    float old_float_value = old_ap->cast_to_float(old_ptype);
-    set_value(new_ptype, this, old_float_value*scale_factor);
+    if (!bitmask) {
+        // Numeric conversion
+        // going via float is safe as the only time we would be converting
+        // from AP_Int32 is when converting to float
+        float old_float_value = old_ap->cast_to_float(old_ptype);
+        set_value(new_ptype, this, old_float_value*scale_factor);
+
+    } else {
+        // Bitmask conversion, go via uint32
+        // int8 -1 should convert to int16 255
+        uint32_t mask;
+        switch (old_ptype) {
+        case AP_PARAM_INT8:
+            mask = (uint8_t)(*(AP_Int8*)old_ap);
+            break;
+        case AP_PARAM_INT16:
+            mask = (uint16_t)(*(AP_Int16*)old_ap);
+            break;
+        case AP_PARAM_INT32:
+            mask = (uint32_t)(*(AP_Int32*)old_ap);
+            break;
+        default:
+            return false;
+        }
+
+        switch (new_ptype) {
+        case AP_PARAM_INT8:
+            ((AP_Int8 *)this)->set(mask);
+            break;
+        case AP_PARAM_INT16:
+            ((AP_Int16 *)this)->set(mask);
+            break;
+        case AP_PARAM_INT32:
+            ((AP_Int32 *)this)->set(mask);
+            break;
+        default:
+            return false;
+        }
+    }
+
 
     // force save as the new type
     save(true);
diff --git a/libraries/AP_Param/AP_Param.h b/libraries/AP_Param/AP_Param.h
index 85d533c1fd..fe85e4175f 100644
--- a/libraries/AP_Param/AP_Param.h
+++ b/libraries/AP_Param/AP_Param.h
@@ -475,11 +475,17 @@ public:
       values without changing the parameter indexes. This will return
       true if the parameter was converted from an old parameter value
     */
-    bool convert_parameter_width(ap_var_type old_ptype, float scale_factor=1.0);
+    bool convert_parameter_width(ap_var_type old_ptype, float scale_factor=1.0) {
+        return _convert_parameter_width(old_ptype, scale_factor, false);
+    }
     bool convert_centi_parameter(ap_var_type old_ptype) {
         return convert_parameter_width(old_ptype, 0.01f);
     }
-    
+    // Converting bitmasks should be done bitwise rather than numerically
+    bool convert_bitmask_parameter_width(ap_var_type old_ptype) {
+        return _convert_parameter_width(old_ptype, 1.0, true);
+    }
+
     // convert a single parameter with scaling
     enum {
         CONVERT_FLAG_REVERSE=1, // handle _REV -> _REVERSED conversion
@@ -765,6 +771,13 @@ private:
     // return true if the parameter is configured in EEPROM/FRAM
     bool configured_in_storage(void) const;
 
+    /*
+      convert width of a parameter, allowing update to wider scalar
+      values without changing the parameter indexes. This will return
+      true if the parameter was converted from an old parameter value
+    */
+    bool _convert_parameter_width(ap_var_type old_ptype, float scale_factor, bool bitmask);
+
     // send a parameter to all GCS instances
     void send_parameter(const char *name, enum ap_var_type param_header_type, uint8_t idx) const;