diff --git a/src/option.h b/src/option.h
index 1ed2a4f..fa5de56 100644
--- a/src/option.h
+++ b/src/option.h
@@ -583,6 +583,9 @@
 EXTERN char_u	*p_mp;		/* 'makeprg' */
 #endif
 EXTERN long	p_mat;		/* 'matchtime' */
+#ifdef FEAT_MBYTE
+EXTERN long	p_mco;		/* 'maxcombine' */
+#endif
 #ifdef FEAT_EVAL
 EXTERN long	p_mfd;		/* 'maxfuncdepth' */
 #endif