4 files changed, 13 insertions, 0 deletions
diff --git a/main.c b/main.c
index 58954f61..768d7dc1 100644
--- a/main.c
+++ b/main.c
@@ -968,6 +968,9 @@ parse(struct mparse *mp, int fd, const char *file,
 		case OUTT_PS:
 			terminal_man(outst->outdata, meta);
 			break;
+		case OUTT_MARKDOWN:
+			mandoc_msg(MANDOCERR_MAN_TMARKDOWN, 0, 0, NULL);
+			break;
 		default:
 			break;
 		}
diff --git a/mandoc.1 b/mandoc.1
index 00d898eb..05026a61 100644
--- a/mandoc.1
+++ b/mandoc.1
@@ -2371,6 +2371,14 @@ The
 .Fl O Cm tag
 option was specified but the tag was not found in any of the displayed
 manual pages.
+.It Sy "\-Tmarkdown unsupported for man(7) input"
+.Pq man
+The
+.Fl T Cm markdown
+option was specified but an input file uses the
+.Xr man 7
+language.
+No output is produced for that input file.
 .El
 .Sh SEE ALSO
 .Xr apropos 1 ,
diff --git a/mandoc.h b/mandoc.h
index 1719eae0..11d0ecfd 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -257,6 +257,7 @@ enum	mandocerr {
 	MANDOCERR_BADVAL_BAD, /* bad argument value */
 	MANDOCERR_BADVAL_DUPE, /* duplicate argument value */
 	MANDOCERR_TAG, /* no such tag */
+	MANDOCERR_MAN_TMARKDOWN, /* -Tmarkdown unsupported for man(7) input */
 
 	MANDOCERR_SYSERR, /* ===== start of system errors ===== */
 
diff --git a/mandoc_msg.c b/mandoc_msg.c
index 8867bb4b..beec5059 100644
--- a/mandoc_msg.c
+++ b/mandoc_msg.c
@@ -257,6 +257,7 @@ static	const char *const type_message[MANDOCERR_MAX] = {
 	"bad option value",
 	"duplicate option value",
 	"no such tag",
+	"-Tmarkdown unsupported for man(7) input",
 
 	/* system errors */
 	NULL,