diff --git a/sys/compat/linuxkpi/common/include/linux/mm.h b/sys/compat/linuxkpi/common/include/linux/mm.h
--- a/sys/compat/linuxkpi/common/include/linux/mm.h
+++ b/sys/compat/linuxkpi/common/include/linux/mm.h
@@ -229,7 +229,7 @@
 	return ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT);
 }
 
-#define	offset_in_page(off)	((off) & (PAGE_SIZE - 1))
+#define	offset_in_page(off)	((unsigned long)(off) & (PAGE_SIZE - 1))
 
 static inline void
 set_page_dirty(struct vm_page *page)