diff --git a/src/dirent/__dirent.h b/src/dirent/__dirent.h
index 101b0368..828a5f17 100644
--- a/src/dirent/__dirent.h
+++ b/src/dirent/__dirent.h
@@ -1,9 +1,11 @@
 struct __dirstream
 {
-	int fd;
 	off_t tell;
+	int fd;
 	int buf_pos;
 	int buf_end;
 	volatile int lock[1];
+	/* Any changes to this struct must preserve the property:
+	 * offsetof(struct __dirent, buf) % sizeof(off_t) == 0 */
 	char buf[2048];
 };
diff --git a/src/dirent/readdir.c b/src/dirent/readdir.c
index 2cf0632c..dc5f3edb 100644
--- a/src/dirent/readdir.c
+++ b/src/dirent/readdir.c
@@ -1,9 +1,13 @@
 #include <dirent.h>
 #include <errno.h>
+#include <stddef.h>
 #include "__dirent.h"
 #include "syscall.h"
 #include "libc.h"
 
+typedef char dirstream_buf_alignment_check[1-2*(int)(
+	offsetof(struct __dirstream, buf) % sizeof(off_t))];
+
 int __getdents(int, struct dirent *, size_t);
 
 struct dirent *readdir(DIR *dir)