diff --git a/racket/src/rktio/configure b/racket/src/rktio/configure
index 3507d3a360..f26d328927 100755
--- a/racket/src/rktio/configure
+++ b/racket/src/rktio/configure
@@ -4256,7 +4256,7 @@ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
    #include <strings.h>
    int main() {
      mbstate_t state;
-     char *src = "X";
+     const char *src = "X";
      bzero(&state, sizeof(mbstate_t));
      mbsrtowcs(0, &src, 0, &state);
      return 0;
diff --git a/racket/src/rktio/configure.ac b/racket/src/rktio/configure.ac
index f9c530cc3d..cebb0a1665 100644
--- a/racket/src/rktio/configure.ac
+++ b/racket/src/rktio/configure.ac
@@ -217,7 +217,7 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([
    #include <strings.h>
    int main() {
      mbstate_t state;
-     char *src = "X";
+     const char *src = "X";
      bzero(&state, sizeof(mbstate_t));
      mbsrtowcs(0, &src, 0, &state);
      return 0;