diff --git a/src/document/html/renderer.c b/src/document/html/renderer.c
index c411e3a5..c94484a2 100644
--- a/src/document/html/renderer.c
+++ b/src/document/html/renderer.c
@@ -8,8 +8,10 @@
  * wcwidth().  Therefore the configure script should have disabled
  * CONFIG_COMBINE if wcwidth() doesn't exist.  */
 #ifdef CONFIG_COMBINE
+#ifndef _XOPEN_SOURCE
 #define _XOPEN_SOURCE 500	/* for wcwidth */
 #endif
+#endif
 
 #include <ctype.h>
 #include <stdarg.h>