diff --git a/src/backend/utils/adt/jsonpath_exec.c b/src/backend/utils/adt/jsonpath_exec.c
index 5c25bc1e430..a758e1a00cb 100644
--- a/src/backend/utils/adt/jsonpath_exec.c
+++ b/src/backend/utils/adt/jsonpath_exec.c
@@ -2130,14 +2130,15 @@ getJsonPathVariable(JsonPathExecContext *cxt, JsonPathItem *variable,
 	JsonbValue	tmp;
 	JsonbValue *v;
 
-	if (!vars)
-	{
-		value->type = jbvNull;
-		return;
-	}
-
 	Assert(variable->type == jpiVariable);
 	varName = jspGetString(variable, &varNameLength);
+
+	if (!vars)
+		ereport(ERROR,
+			(errcode(ERRCODE_UNDEFINED_OBJECT),
+			 errmsg("could not find jsonpath variable \"%s\"",
+					pnstrdup(varName, varNameLength))));
+
 	tmp.type = jbvString;
 	tmp.val.string.val = varName;
 	tmp.val.string.len = varNameLength;
diff --git a/src/test/regress/expected/jsonb_jsonpath.out b/src/test/regress/expected/jsonb_jsonpath.out
index 6659bc9091a..eafb421c7af 100644
--- a/src/test/regress/expected/jsonb_jsonpath.out
+++ b/src/test/regress/expected/jsonb_jsonpath.out
@@ -487,6 +487,13 @@ select * from jsonb_path_query('{"a": 10}', '$');
 
 select * from jsonb_path_query('{"a": 10}', '$ ? (@.a < $value)');
 ERROR:  could not find jsonpath variable "value"
+-- the @? and @@ operators supply no variables, so a variable reference
+-- must be reported as undefined rather than silently treated as NULL
+-- (the latter gave wrong results and could drive unbounded memory use)
+select jsonb '42' @? '$"no_such_var"';
+ERROR:  could not find jsonpath variable "no_such_var"
+select jsonb '42' @@ '$"no_such_var" == 1';
+ERROR:  could not find jsonpath variable "no_such_var"
 select * from jsonb_path_query('{"a": 10}', '$ ? (@.a < $value)', '1');
 ERROR:  "vars" argument is not an object
 DETAIL:  Jsonpath parameters should be encoded as key-value pairs of "vars" object.
diff --git a/src/test/regress/sql/jsonb_jsonpath.sql b/src/test/regress/sql/jsonb_jsonpath.sql
index e0ce509264a..8163fc6713b 100644
--- a/src/test/regress/sql/jsonb_jsonpath.sql
+++ b/src/test/regress/sql/jsonb_jsonpath.sql
@@ -98,6 +98,11 @@ select jsonb_path_query('[1,2,3]', '$[last ? (@.type() == "string")]', silent =>
 
 select * from jsonb_path_query('{"a": 10}', '$');
 select * from jsonb_path_query('{"a": 10}', '$ ? (@.a < $value)');
+-- the @? and @@ operators supply no variables, so a variable reference
+-- must be reported as undefined rather than silently treated as NULL
+-- (the latter gave wrong results and could drive unbounded memory use)
+select jsonb '42' @? '$"no_such_var"';
+select jsonb '42' @@ '$"no_such_var" == 1';
 select * from jsonb_path_query('{"a": 10}', '$ ? (@.a < $value)', '1');
 select * from jsonb_path_query('{"a": 10}', '$ ? (@.a < $value)', '[{"value" : 13}]');
 select * from jsonb_path_query('{"a": 10}', '$ ? (@.a < $value)', '{"value" : 13}');