diff --git a/Makefile b/Makefile
index 11b78c3..8f820e1 100644
--- a/Makefile
+++ b/Makefile
@@ -127,7 +127,7 @@ _forktest: forktest.o $(ULIB)
 	$(OBJDUMP) -S _forktest > forktest.asm
 
 mkfs: mkfs.c fs.h
-	gcc -Wall -o mkfs mkfs.c
+	gcc -m32 -Werror -Wall -o mkfs mkfs.c
 
 UPROGS=\
 	_cat\
diff --git a/mkfs.c b/mkfs.c
index 3a3c62a..a970b5c 100644
--- a/mkfs.c
+++ b/mkfs.c
@@ -82,7 +82,7 @@ main(int argc, char *argv[])
   usedblocks = ninodes / IPB + 3 + bitblocks;
   freeblock = usedblocks;
 
-  printf("used %d (bit %d ninode %lu) free %u total %d\n", usedblocks,
+  printf("used %d (bit %d ninode %u) free %u total %d\n", usedblocks,
          bitblocks, ninodes/IPB + 1, freeblock, nblocks+usedblocks);
 
   assert(nblocks + usedblocks == size);
@@ -230,7 +230,7 @@ balloc(int used)
   for(i = 0; i < used; i++) {
     buf[i/8] = buf[i/8] | (0x1 << (i%8));
   }
-  printf("balloc: write bitmap block at sector %lu\n", ninodes/IPB + 3);
+  printf("balloc: write bitmap block at sector %u\n", ninodes/IPB + 3);
   wsect(ninodes / IPB + 3, buf);
 }