diff --git a/config.h.in b/config.h.in
index 47773a5..903db9c 100644
--- a/config.h.in
+++ b/config.h.in
@@ -96,6 +96,9 @@
 /* Define if you have POSIX threads */
 #undef _POSIX_THREADS
 
+/* Define to force use of thread-safe errno, h_errno, and other functions */
+#undef _REENTRANT
+
 /* Define if setpgrp() must be called as setpgrp(0, 0). */
 #undef SETPGRP_HAVE_ARG