diff --git a/src/lib/ares_setup.h b/src/lib/ares_setup.h
index e8d39548..0387f3e3 100644
--- a/src/lib/ares_setup.h
+++ b/src/lib/ares_setup.h
@@ -138,8 +138,9 @@
  * undefine USE_WINSOCK.
  */
 
-#undef USE_WINSOCK
-
+#ifdef USE_WINSOCK
+#  undef USE_WINSOCK
+#endif
 #ifdef HAVE_WINSOCK2_H
 #  define USE_WINSOCK 2
 #else
@@ -203,13 +204,27 @@
  *  --enable-debug) so we undef them again here.
  */
 
-#undef PACKAGE_STRING
-#undef PACKAGE_TARNAME
-#undef PACKAGE_VERSION
-#undef PACKAGE_BUGREPORT
-#undef PACKAGE_NAME
-#undef VERSION
-#undef PACKAGE
+#ifdef PACKAGE_STRING
+#  undef PACKAGE_STRING
+#endif
+#ifdef PACKAGE_TARNAME
+#  undef PACKAGE_TARNAME
+#endif
+#ifdef PACKAGE_VERSION
+#  undef PACKAGE_VERSION
+#endif
+#ifdef PACKAGE_BUGREPORT
+#  undef PACKAGE_BUGREPORT
+#endif
+#ifdef PACKAGE_NAME
+#  undef PACKAGE_NAME
+#endif
+#ifdef VERSION
+#  undef VERSION
+#endif
+#ifdef PACKAGE
+#  undef PACKAGE
+#endif
 
 /* IPv6 compatibility */
 #if !defined(HAVE_AF_INET6)
diff --git a/src/tools/ares_getopt.h b/src/tools/ares_getopt.h
index 040184e6..b80da752 100644
--- a/src/tools/ares_getopt.h
+++ b/src/tools/ares_getopt.h
@@ -35,11 +35,21 @@
 
 int ares_getopt(int nargc, char * const nargv[], const char *ostr);
 
-#undef optarg
-#undef optind
-#undef opterr
-#undef optopt
-#undef optreset
+#ifdef optarg
+#  undef optarg
+#endif
+#ifdef optind
+#  undef optind
+#endif
+#ifdef opterr
+#  undef opterr
+#endif
+#ifdef optopt
+#  undef optopt
+#endif
+#ifdef optreset
+#  undef optreset
+#endif
 
 #define optarg   ares_optarg
 #define optind   ares_optind