diff --git a/src/system/kernel/heap.cpp b/src/system/kernel/heap.cpp
index 0720773e37..f90e24aefe 100644
--- a/src/system/kernel/heap.cpp
+++ b/src/system/kernel/heap.cpp
@@ -54,13 +54,13 @@ typedef struct heap_page_s {
 	uint16			in_use : 1;
 	heap_page_s *	next;
 	heap_page_s *	prev;
-	uint16			empty_index;
+	union {
+		uint16			empty_index;
+		uint16			allocation_id; // used for bin == bin_count allocations
+	};
 	addr_t *		free_list;
 } heap_page;
 
-// used for bin == bin_count allocations
-#define allocation_id empty_index
-
 typedef struct heap_bin_s {
 	uint32		element_size;
 	uint16		max_free_count;