diff --git a/src/chars.c b/src/chars.c
index fcbc9f4f..9ea0bc07 100644
--- a/src/chars.c
+++ b/src/chars.c
@@ -712,17 +712,3 @@ bool is_valid_unicode(wchar_t wc)
 				(0xFFFF < wc && wc <= 0x10FFFF && (wc & 0xFFFF) <= 0xFFFD));
 }
 #endif
-
-#ifdef ENABLE_NANORC
-/* Check if the string s is a valid multibyte string.  Return TRUE if it
- * is, and FALSE otherwise. */
-bool is_valid_mbstring(const char *s)
-{
-#ifdef ENABLE_UTF8
-	if (use_utf8)
-		return (mbstowcs(NULL, s, 0) != (size_t)-1);
-	else
-#endif
-		return TRUE;
-}
-#endif /* ENABLE_NANORC */
diff --git a/src/proto.h b/src/proto.h
index 399725a8..30d18a75 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -236,9 +236,6 @@ bool has_blank_mbchars(const char *s);
 #ifdef ENABLE_UTF8
 bool is_valid_unicode(wchar_t wc);
 #endif
-#ifdef ENABLE_NANORC
-bool is_valid_mbstring(const char *s);
-#endif
 
 /* Most functions in color.c. */
 #ifdef ENABLE_COLOR
diff --git a/src/rcfile.c b/src/rcfile.c
index 2e6675ea..4ab8241f 100644
--- a/src/rcfile.c
+++ b/src/rcfile.c
@@ -1085,12 +1085,13 @@ void parse_rcfile(FILE *rcstream, bool syntax_only)
 #ifdef DEBUG
 		fprintf(stderr, "    Option argument = \"%s\"\n", option);
 #endif
-		/* Make sure the option argument is a valid multibyte string. */
-		if (!is_valid_mbstring(option)) {
+#ifdef ENABLE_UTF8
+		/* When in a UTF-8 locale, ignore arguments with invalid sequences. */
+		if (using_utf8() && mbstowcs(NULL, option, 0) == (size_t)-1) {
 			rcfile_error(N_("Argument is not a valid multibyte string"));
 			continue;
 		}
-
+#endif
 #ifdef ENABLE_COLOR
 		if (strcasecmp(rcopts[i].name, "titlecolor") == 0)
 			color_combo[TITLE_BAR] = parse_interface_color(option);