diff --git a/ctp-validators/src/main/kotlin/com/commercetools/rmf/validators/DiscriminatedSubtypeRule.kt b/ctp-validators/src/main/kotlin/com/commercetools/rmf/validators/DiscriminatedSubtypeRule.kt
new file mode 100644
index 00000000..beade954
--- /dev/null
+++ b/ctp-validators/src/main/kotlin/com/commercetools/rmf/validators/DiscriminatedSubtypeRule.kt
@@ -0,0 +1,41 @@
+package com.commercetools.rmf.validators
+
+import io.vrap.rmf.raml.model.types.ObjectType
+import org.eclipse.emf.common.util.Diagnostic
+import java.util.ArrayList
+import java.util.Locale
+
+@ValidatorSet
+class DiscriminatedSubtypeRule(severity: RuleSeverity, options: List<RuleOption>? = null) : TypesRule(severity, options)  {
+
+    // implement
+    private val exclude: List<String> =
+        (options?.filter { ruleOption -> ruleOption.type.lowercase(Locale.getDefault()) == RuleOptionType.EXCLUDE.toString() }?.map { ruleOption -> ruleOption.value }?.plus("") ?: defaultExcludes)
+
+    // implement
+    override fun caseObjectType(type: ObjectType): List<Diagnostic> {
+        val validationResults: MutableList<Diagnostic> = ArrayList()
+
+        val parent = type.type
+        if (!type.isInlineType && parent != null && (parent as ObjectType).discriminator != null && type.discriminatorValue == null && exclude.contains(type.name).not()) {
+            validationResults.add(create(type,
+                "Discriminator was added to supertype, it should be set to not null for all subtypes. Discriminator is set to null for subtype: {0}, while there is a discriminator for parent type: {1}",
+                type.name, parent.name))
+        }
+
+        return validationResults
+    }
+
+    companion object : ValidatorFactory<DiscriminatedSubtypeRule> {
+        private val defaultExcludes by lazy { listOf("") }
+
+        @JvmStatic
+        override fun create(options: List<RuleOption>?): DiscriminatedSubtypeRule {
+            return DiscriminatedSubtypeRule(RuleSeverity.ERROR, options)
+        }
+
+        @JvmStatic
+        override fun create(severity: RuleSeverity, options: List<RuleOption>?): DiscriminatedSubtypeRule {
+            return DiscriminatedSubtypeRule(severity, options)
+        }    }
+}
\ No newline at end of file
diff --git a/ctp-validators/src/test/groovy/com/commercetools/rmf/validators/ValidatorRulesTest.groovy b/ctp-validators/src/test/groovy/com/commercetools/rmf/validators/ValidatorRulesTest.groovy
index 9e7c78fc..8f25e415 100644
--- a/ctp-validators/src/test/groovy/com/commercetools/rmf/validators/ValidatorRulesTest.groovy
+++ b/ctp-validators/src/test/groovy/com/commercetools/rmf/validators/ValidatorRulesTest.groovy
@@ -81,6 +81,16 @@ class ValidatorRulesTest extends Specification implements ValidatorFixtures {
         result.validationResults[0].message == "Discriminator and DiscriminatorValue property defined in the same type: InvalidFooBaz"
     }
 
+    def "discriminator subtype rule"() {
+        def validators = Arrays.asList(new TypesValidator(Arrays.asList(DiscriminatedSubtypeRule.create(emptyList()))))
+        def uri = uriFromClasspath("/discriminatorsubtype-rule.raml")
+        when:
+        def result = new RamlModelBuilder(validators).buildApi(uri)
+        then:
+        result.validationResults.size() == 1
+        result.validationResults[0].message == "Discriminator was added to supertype, it should be set to not null for all subtypes. Discriminator is set to null for subtype: InvalidFoo, while there is a discriminator for parent type: Foo"
+    }
+
     def "filename rule"() {
         when:
         def validators = Arrays.asList(new ModulesValidator(Arrays.asList(FilenameRule.create(emptyList()))))
diff --git a/ctp-validators/src/test/resources/discriminatorsubtype-rule.raml b/ctp-validators/src/test/resources/discriminatorsubtype-rule.raml
new file mode 100644
index 00000000..1dcd3513
--- /dev/null
+++ b/ctp-validators/src/test/resources/discriminatorsubtype-rule.raml
@@ -0,0 +1,35 @@
+#%RAML 1.0
+title: discriminator parent rule
+
+types:
+  Foo:
+    description: Foo
+    type: object
+    discriminator: type
+    properties:
+      type: string
+  FooBar:
+    description: FooBar
+    type: Foo
+    discriminatorValue: foobar
+  InvalidFoo:
+    description: FooBar
+    type: Foo
+    properties:
+      type: string
+  ValidProperty:
+    type: object
+    properties:
+      foo:
+        type: Foo
+        description: foo
+      fooBar:
+        type: FooBar
+        description: foobar
+
+/test:
+  post:
+    body:
+      application/json:
+        type: Foo
+        description: foo