diff --git a/src/alloc.c b/src/alloc.c
index 1eee1f2f..7be1a6e9 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -40,6 +40,7 @@ extern inline void* _mi_page_malloc_zero(mi_heap_t* heap, mi_page_t* page, size_
   page->free = mi_block_next(page, block);
   page->used++;
   mi_assert_internal(page->free == NULL || _mi_ptr_page(page->free) == page);
+  mi_assert_internal(_mi_is_aligned(block, MI_MAX_ALIGN_SIZE));
   #if MI_DEBUG>3
   if (page->free_is_zero) {
     mi_assert_expensive(mi_mem_is_zero(block+1,size - sizeof(*block)));
diff --git a/src/segment.c b/src/segment.c
index 54a917ea..d9631d48 100644
--- a/src/segment.c
+++ b/src/segment.c
@@ -436,6 +436,8 @@ uint8_t* _mi_segment_page_start(const mi_segment_t* segment, const mi_page_t* pa
       mi_assert_internal((uintptr_t)p % block_size == 0);
     }
   }
+  mi_assert_internal(_mi_is_aligned(p, MI_MAX_ALIGN_SIZE));
+  mi_assert_internal(block_size > MI_MAX_ALIGN_GUARANTEE || _mi_is_aligned(p,block_size));
 
   if (page_size != NULL) *page_size = psize;
   mi_assert_internal(_mi_ptr_page(p) == page);