diff --git a/src/common/compat.c b/src/common/compat.c
index 74585cd614..2a4763c0fc 100644
--- a/src/common/compat.c
+++ b/src/common/compat.c
@@ -429,7 +429,6 @@ tor_vasprintf(char **strp, const char *fmt, va_list args)
   /* On Windows, _vsnprintf won't tell us the length of the string if it
    * overflows, so we need to use _vcsprintf to tell how much to allocate */
   int len, r;
-  char *res;
   len = _vscprintf(fmt, args);
   if (len < 0) {
     *strp = NULL;