diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
index 350bc07f210..64147bc5b5c 100644
--- a/src/backend/utils/adt/like.c
+++ b/src/backend/utils/adt/like.c
@@ -191,12 +191,14 @@ Generic_Text_IC_like(text *str, text *pat, Oid collation)
 
 	/*
 	 * For efficiency reasons, in the C locale we don't call lower() on the
-	 * pattern and text, but instead lowercase each character lazily.
+	 * pattern and text, but instead lowercase each character lazily. This
+	 * only works for single-byte encodings, otherwise "_" may incorrectly
+	 * match an incomplete byte sequence.
 	 *
 	 * XXX: use casefolding instead?
 	 */
 
-	if (locale->ctype_is_c)
+	if (locale->ctype_is_c && pg_database_encoding_max_length() == 1)
 	{
 		p = VARDATA_ANY(pat);
 		plen = VARSIZE_ANY_EXHDR(pat);
diff --git a/src/test/regress/expected/collate.utf8.out b/src/test/regress/expected/collate.utf8.out
index 99fdc111fa4..cdd1a37ba18 100644
--- a/src/test/regress/expected/collate.utf8.out
+++ b/src/test/regress/expected/collate.utf8.out
@@ -34,6 +34,13 @@ SELECT U&'\00C1\00E1' !~ '[[:alpha:]]' COLLATE regress_builtin_c;
 (1 row)
 
 DROP COLLATION regress_builtin_c;
+-- a '_' matches a multibyte character
+SELECT 'café' ILIKE 'caf_' COLLATE "C";
+ ?column? 
+----------
+ t
+(1 row)
+
 --
 -- Test PG_C_UTF8
 --
diff --git a/src/test/regress/sql/collate.utf8.sql b/src/test/regress/sql/collate.utf8.sql
index 22aecee3a60..52cf068dd0c 100644
--- a/src/test/regress/sql/collate.utf8.sql
+++ b/src/test/regress/sql/collate.utf8.sql
@@ -26,6 +26,9 @@ SELECT U&'\00C1\00E1' !~ '[[:alpha:]]' COLLATE regress_builtin_c;
 
 DROP COLLATION regress_builtin_c;
 
+-- a '_' matches a multibyte character
+SELECT 'café' ILIKE 'caf_' COLLATE "C";
+
 --
 -- Test PG_C_UTF8
 --