diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index 0ae8e04ef82..45f9a14a957 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -631,8 +631,13 @@ EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '$[$[:alnum:]$]$'
 (2 rows)
 
 -- Opening parenthesis "("
-EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '([([:alnum:](](';
-ERROR:  invalid regular expression: parentheses () not balanced
+EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '()[([:alnum:](]()';
+                      QUERY PLAN                      
+------------------------------------------------------
+ Seq Scan on text_tbl
+   Filter: (f1 ~ '^(?:(?:)[([:alnum:](](?:))$'::text)
+(2 rows)
+
 -- Caret "^"
 EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '^[^[:alnum:]^[^^][[^^]][\^][[\^]]\^]^';
                                QUERY PLAN                               
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index 8fb80ed3061..faa43caee2e 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -204,7 +204,7 @@ EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '.[.[:alnum:].].'
 -- Dollar "$"
 EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '$[$[:alnum:]$]$';
 -- Opening parenthesis "("
-EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '([([:alnum:](](';
+EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '()[([:alnum:](]()';
 -- Caret "^"
 EXPLAIN (COSTS OFF) SELECT * FROM TEXT_TBL WHERE f1 SIMILAR TO '^[^[:alnum:]^[^^][[^^]][\^][[\^]]\^]^';
 -- Closing square bracket "]" at the beginning of character class