diff --git a/include/mimalloc/types.h b/include/mimalloc/types.h
index 69f737b3..4540998f 100644
--- a/include/mimalloc/types.h
+++ b/include/mimalloc/types.h
@@ -75,7 +75,7 @@ terms of the MIT license. A copy of the license can be found in the file
 
 // Use guard pages behind objects of a certain size (set by the MIMALLOC_DEBUG_GUARDED_MIN/MAX options)
 // Padding should be disabled when using guard pages
-// #define MI_DEBUG_GUARDED 1
+#define MI_DEBUG_GUARDED 1
 #if defined(MI_DEBUG_GUARDED)
 #define MI_PADDING  0
 #endif
diff --git a/src/segment.c b/src/segment.c
index 8a62329f..1f1dc006 100644
--- a/src/segment.c
+++ b/src/segment.c
@@ -332,6 +332,7 @@ static uint8_t* _mi_segment_page_start_from_slice(const mi_segment_t* segment, c
     if (block_size <= 64) { start_offset += 3*block_size; }
     else if (block_size <= 512) { start_offset += block_size; }
   }
+  start_offset = _mi_align_up(start_offset, MI_MAX_ALIGN_SIZE);
   mi_assert_internal(_mi_is_aligned(pstart + start_offset, MI_MAX_ALIGN_SIZE));
   mi_assert_internal(block_size == 0 || block_size > MI_MAX_ALIGN_GUARANTEE || _mi_is_aligned(pstart + start_offset,block_size));
   if (page_size != NULL) { *page_size = psize - start_offset; }