diff --git a/include/mimalloc/types.h b/include/mimalloc/types.h
index c7ddaaae..b3e51e61 100644
--- a/include/mimalloc/types.h
+++ b/include/mimalloc/types.h
@@ -172,7 +172,7 @@ typedef int32_t  mi_ssize_t;
 // Derived constants
 #define MI_SEGMENT_SIZE                   (MI_ZU(1)<<MI_SEGMENT_SHIFT)
 #define MI_SEGMENT_ALIGN                  MI_SEGMENT_SIZE
-#define MI_SEGMENT_MASK                   (MI_SEGMENT_ALIGN - 1)
+#define MI_SEGMENT_MASK                   ((uintptr_t)(MI_SEGMENT_ALIGN - 1))
 #define MI_SEGMENT_SLICE_SIZE             (MI_ZU(1)<< MI_SEGMENT_SLICE_SHIFT)
 #define MI_SLICES_PER_SEGMENT             (MI_SEGMENT_SIZE / MI_SEGMENT_SLICE_SIZE) // 1024