diff --git a/libraries/AP_HAL/Util.h b/libraries/AP_HAL/Util.h
index f5e116a593..678b06fc51 100644
--- a/libraries/AP_HAL/Util.h
+++ b/libraries/AP_HAL/Util.h
@@ -153,7 +153,7 @@ public:
 #ifdef ENABLE_HEAP
     // heap functions, note that a heap once alloc'd cannot be dealloc'd
     virtual void *allocate_heap_memory(size_t size) = 0;
-    virtual void *heap_realloc(void *heap, void *ptr, size_t new_size) = 0;
+    virtual void *heap_realloc(void *heap, void *ptr, size_t old_size, size_t new_size) = 0;
 #if USE_LIBC_REALLOC
     virtual void *std_realloc(void *ptr, size_t new_size) { return realloc(ptr, new_size); }
 #else