1 files changed, 1 insertions, 0 deletions
diff --git a/mandoc.h b/mandoc.h
index 166483b3..46a50be8 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -48,6 +48,7 @@ enum	mandocerr {
 
 	MANDOCERR_MDOCDATE, /* Mdocdate found: Dd ... */
 	MANDOCERR_MDOCDATE_MISSING, /* Mdocdate missing: Dd ... */
+	MANDOCERR_OS_ARG,  /* operating system explicitly specified: Os ... */
 	MANDOCERR_RCS_MISSING, /* RCS id missing */
 
 	MANDOCERR_STYLE, /* ===== start of style suggestions ===== */