diff --git a/src/common/wchar.c b/src/common/wchar.c
index 5631e2c9363..191f3552ed3 100644
--- a/src/common/wchar.c
+++ b/src/common/wchar.c
@@ -267,12 +267,22 @@ pg_euccn2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
 	return cnt;
 }
 
+/*
+ * mbverifychar does not accept SS2 or SS3 (CS2 and CS3 are not defined for
+ * EUC_CN), but mb2wchar_with_len does.  Tell a coherent story for code that
+ * relies on agreement between mb2wchar_with_len and mblen.  Invalid text
+ * datums (e.g. from shared catalogs) reach this.
+ */
 static int
 pg_euccn_mblen(const unsigned char *s)
 {
 	int			len;
 
-	if (IS_HIGHBIT_SET(*s))
+	if (*s == SS2)
+		len = 3;
+	else if (*s == SS3)
+		len = 3;
+	else if (IS_HIGHBIT_SET(*s))
 		len = 2;
 	else
 		len = 1;
@@ -2064,7 +2074,7 @@ pg_encoding_set_invalid(int encoding, char *dst)
 const pg_wchar_tbl pg_wchar_table[] = {
 	[PG_SQL_ASCII] = {pg_ascii2wchar_with_len, pg_wchar2single_with_len, pg_ascii_mblen, pg_ascii_dsplen, pg_ascii_verifychar, pg_ascii_verifystr, 1},
 	[PG_EUC_JP] = {pg_eucjp2wchar_with_len, pg_wchar2euc_with_len, pg_eucjp_mblen, pg_eucjp_dsplen, pg_eucjp_verifychar, pg_eucjp_verifystr, 3},
-	[PG_EUC_CN] = {pg_euccn2wchar_with_len, pg_wchar2euc_with_len, pg_euccn_mblen, pg_euccn_dsplen, pg_euccn_verifychar, pg_euccn_verifystr, 2},
+	[PG_EUC_CN] = {pg_euccn2wchar_with_len, pg_wchar2euc_with_len, pg_euccn_mblen, pg_euccn_dsplen, pg_euccn_verifychar, pg_euccn_verifystr, 3},
 	[PG_EUC_KR] = {pg_euckr2wchar_with_len, pg_wchar2euc_with_len, pg_euckr_mblen, pg_euckr_dsplen, pg_euckr_verifychar, pg_euckr_verifystr, 3},
 	[PG_EUC_TW] = {pg_euctw2wchar_with_len, pg_wchar2euc_with_len, pg_euctw_mblen, pg_euctw_dsplen, pg_euctw_verifychar, pg_euctw_verifystr, 4},
 	[PG_EUC_JIS_2004] = {pg_eucjp2wchar_with_len, pg_wchar2euc_with_len, pg_eucjp_mblen, pg_eucjp_dsplen, pg_eucjp_verifychar, pg_eucjp_verifystr, 3},