diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index d6efd07073a..cbc70fde716 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -5295,6 +5295,14 @@ convert_string_datum(Datum value, Oid typid, Oid collid, bool *failure)
 			return NULL;
 	}
 
+	/*
+	 * If we don't have a collation, act as though it's "C".  This would
+	 * normally happen only for the "char" type, but perhaps there are other
+	 * cases.
+	 */
+	if (!OidIsValid(collid))
+		return val;
+
 	mylocale = pg_newlocale_from_collation(collid);
 
 	if (!mylocale->collate_is_c)
diff --git a/src/test/regress/expected/planner_est.out b/src/test/regress/expected/planner_est.out
index b62a47552fa..236cb274a78 100644
--- a/src/test/regress/expected/planner_est.out
+++ b/src/test/regress/expected/planner_est.out
@@ -210,4 +210,15 @@ false, true, false, true);
      ->  Result  (cost=N..N rows=1 width=N)
 (4 rows)
 
+-- Verify that scalarineqsel() works on "char" columns
+CREATE TEMP TABLE char_table_1 AS
+  SELECT i::"char" AS c FROM generate_series(64,96) i;
+ANALYZE char_table_1;
+EXPLAIN (COSTS OFF) SELECT * FROM char_table_1 WHERE c < 'Q';
+         QUERY PLAN          
+-----------------------------
+ Seq Scan on char_table_1
+   Filter: (c < 'Q'::"char")
+(2 rows)
+
 DROP FUNCTION explain_mask_costs(text, bool, bool, bool, bool);
diff --git a/src/test/regress/sql/planner_est.sql b/src/test/regress/sql/planner_est.sql
index 53210d5baad..2b696a4e4e5 100644
--- a/src/test/regress/sql/planner_est.sql
+++ b/src/test/regress/sql/planner_est.sql
@@ -147,4 +147,10 @@ SELECT explain_mask_costs($$
 SELECT * FROM tenk1 WHERE unique1 <> ALL (ARRAY[1, 2, 98, (SELECT 99), NULL]);$$,
 false, true, false, true);
 
+-- Verify that scalarineqsel() works on "char" columns
+CREATE TEMP TABLE char_table_1 AS
+  SELECT i::"char" AS c FROM generate_series(64,96) i;
+ANALYZE char_table_1;
+EXPLAIN (COSTS OFF) SELECT * FROM char_table_1 WHERE c < 'Q';
+
 DROP FUNCTION explain_mask_costs(text, bool, bool, bool, bool);