diff --git a/midx.c b/midx.c
index c13c6f9d72..db9c49bb2b 100644
--- a/midx.c
+++ b/midx.c
@@ -236,7 +236,7 @@ static off_t nth_midxed_offset(struct multi_pack_index *m, uint32_t pos)
 	offset32 = get_be32(offset_data + sizeof(uint32_t));
 
 	if (m->chunk_large_offsets && offset32 & MIDX_LARGE_OFFSET_NEEDED) {
-		if (sizeof(offset32) < sizeof(uint64_t))
+		if (sizeof(off_t) < sizeof(uint64_t))
 			die(_("multi-pack-index stores a 64-bit offset, but off_t is too small"));
 
 		offset32 ^= MIDX_LARGE_OFFSET_NEEDED;