diff --git a/usr/src/cmd/troff/n1.c b/usr/src/cmd/troff/n1.c
index f1f2f001343e..a003ea77a9af 100644
--- a/usr/src/cmd/troff/n1.c
+++ b/usr/src/cmd/troff/n1.c
@@ -850,6 +850,8 @@ getch()
 	case 'e':	/* printable version of current eschar */
 		i = PRESC;
 		goto gx;
+	case '~':	/* Heirloom/groff/neatroff: unbreakable space */
+		; /* fall through */
 	case ' ':	/* unpaddable space */
 		i = UNPAD;
 		goto gx;