diff --git a/zpa-core/src/main/kotlin/org/sonar/plugins/plsqlopen/api/ConditionsGrammar.kt b/zpa-core/src/main/kotlin/org/sonar/plugins/plsqlopen/api/ConditionsGrammar.kt
index a5835705..7df84ce3 100644
--- a/zpa-core/src/main/kotlin/org/sonar/plugins/plsqlopen/api/ConditionsGrammar.kt
+++ b/zpa-core/src/main/kotlin/org/sonar/plugins/plsqlopen/api/ConditionsGrammar.kt
@@ -74,7 +74,7 @@ enum class ConditionsGrammar : GrammarRuleKey {
             ).skip()
 
             b.rule(BOOLEAN_TEST_CONDITION).define(
-                CONCATENATION_EXPRESSION, IS, b.optional(NOT), b.firstOf(NULL_LITERAL, TRUE, FALSE)
+                CONCATENATION_EXPRESSION, IS, b.optional(NOT), b.firstOf(NULL_LITERAL, PlSqlGrammar.BOOLEAN_LITERAL)
             )
 
             b.rule(LIKE_CONDITION).define(