diff --git a/include/mimalloc/types.h b/include/mimalloc/types.h
index 28343d21..bef23d51 100644
--- a/include/mimalloc/types.h
+++ b/include/mimalloc/types.h
@@ -165,7 +165,7 @@ 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_SMALL_PAGE_SIZE                (MI_ZU(1)<<MI_SMALL_PAGE_SHIFT)
 #define MI_MEDIUM_PAGE_SIZE               (MI_ZU(1)<<MI_MEDIUM_PAGE_SHIFT)