diff --git a/portable/MemMang/heap_5.c b/portable/MemMang/heap_5.c
index bf321304f..a54381b0c 100644
--- a/portable/MemMang/heap_5.c
+++ b/portable/MemMang/heap_5.c
@@ -284,7 +284,14 @@ void * pvPortMalloc( size_t xWantedSize )
                 {
                     pxPreviousBlock = pxBlock;
                     pxBlock = heapPROTECT_BLOCK_POINTER( pxBlock->pxNextFreeBlock );
-                    heapVALIDATE_BLOCK_POINTER( pxBlock );
+
+                    /* pxEnd is the end marker of the free list. It is located at
+                     * pucHeapHighAddress and is not part of the usable heap, so it
+                     * must be excluded from the heap block pointer validation. */
+                    if( pxBlock != pxEnd )
+                    {
+                        heapVALIDATE_BLOCK_POINTER( pxBlock );
+                    }
                 }
 
                 /* If the end marker was reached then a block of adequate size