diff --git a/sha1_file.c b/sha1_file.c
index 25f6965294..797b0634ce 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1070,6 +1070,11 @@ static void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 
 		if (!fstat(fd, &st)) {
 			*size = xsize_t(st.st_size);
+			if (!*size) {
+				/* mmap() is forbidden on empty files */
+				error("object file %s is empty", sha1_file_name(sha1));
+				return NULL;
+			}
 			map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
 		}
 		close(fd);