diff --git a/Zend/zend_alloc.c b/Zend/zend_alloc.c
index 7e83f067a4f..5dcf7ce5d71 100644
--- a/Zend/zend_alloc.c
+++ b/Zend/zend_alloc.c
@@ -2401,6 +2401,18 @@ void* ZEND_FASTCALL _zend_mm_realloc2(zend_mm_heap *heap, void *ptr, size_t size
 
 ZEND_API size_t ZEND_FASTCALL _zend_mm_block_size(zend_mm_heap *heap, void *ptr ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC)
 {
+#if ZEND_MM_CUSTOM
+	if (UNEXPECTED(heap->use_custom_heap)) {
+		if (heap->custom_heap.std._malloc == tracked_malloc) {
+			zend_ulong h = ((uintptr_t) ptr) >> ZEND_MM_ALIGNMENT_LOG2;
+			zval *size_zv = zend_hash_index_find(heap->tracked_allocs, h);
+			if  (size_zv) {
+				return Z_LVAL_P(size_zv);
+			}
+		}
+		return 0;
+	}
+#endif
 	return zend_mm_size(heap, ptr ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_ORIG_RELAY_CC);
 }
 
@@ -2636,12 +2648,7 @@ ZEND_API void* ZEND_FASTCALL _erealloc2(void *ptr, size_t size, size_t copy_size
 
 ZEND_API size_t ZEND_FASTCALL _zend_mem_block_size(void *ptr ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC)
 {
-#if ZEND_MM_CUSTOM
-	if (UNEXPECTED(AG(mm_heap)->use_custom_heap)) {
-		return 0;
-	}
-#endif
-	return zend_mm_size(AG(mm_heap), ptr ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_ORIG_RELAY_CC);
+	return _zend_mm_block_size(AG(mm_heap), ptr ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_ORIG_RELAY_CC);
 }
 
 ZEND_API void* ZEND_FASTCALL _safe_emalloc(size_t nmemb, size_t size, size_t offset ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC)