diff --git a/libisoburn/trunk/test/compare_file.c b/libisoburn/trunk/test/compare_file.c
index 8a450ba9..2d460f54 100644
--- a/libisoburn/trunk/test/compare_file.c
+++ b/libisoburn/trunk/test/compare_file.c
@@ -266,7 +266,8 @@ int main(int argc, char **argv)
  }
  strcpy(adr1, argv[1]);
  strcpy(adrc, argv[1]+strlen(argv[2]));
- sprintf(adr2, "%s%s%s", argv[3], (adrc[0]=='/' ? "" : "/"), adrc);
+ sprintf(adr2, "%s%s%s",
+         argv[3], (adrc[0]=='/' || adrc[0]==0 ? "" : "/"), adrc);
 
  ret=  Compare_2_files(adr1, adr2, adrc, (with_ctime<<1));
  exit(ret<=0);