diff --git a/python/python-psi-api/src/com/jetbrains/python/psi/PyWithAncestors.java b/python/python-psi-api/src/com/jetbrains/python/psi/PyWithAncestors.java
index 354ec7580157..c0b4f875e149 100644
--- a/python/python-psi-api/src/com/jetbrains/python/psi/PyWithAncestors.java
+++ b/python/python-psi-api/src/com/jetbrains/python/psi/PyWithAncestors.java
@@ -19,6 +19,7 @@ import com.jetbrains.python.ast.PyAstWithAncestors;
 import com.jetbrains.python.psi.types.PyClassLikeType;
 import com.jetbrains.python.psi.types.TypeEvalContext;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.List;
 
@@ -32,5 +33,5 @@ public interface PyWithAncestors extends PyAstWithAncestors {
    * Returns types of all ancestors from the hierarchy.
    */
   @NotNull
-  List<PyClassLikeType> getAncestorTypes(@NotNull TypeEvalContext context);
+  List<@Nullable PyClassLikeType> getAncestorTypes(@NotNull TypeEvalContext context);
 }
diff --git a/python/python-psi-impl/src/com/jetbrains/python/inspections/PyInvalidCastInspection.kt b/python/python-psi-impl/src/com/jetbrains/python/inspections/PyInvalidCastInspection.kt
index b4b8154abf59..d3e142300302 100644
--- a/python/python-psi-impl/src/com/jetbrains/python/inspections/PyInvalidCastInspection.kt
+++ b/python/python-psi-impl/src/com/jetbrains/python/inspections/PyInvalidCastInspection.kt
@@ -83,7 +83,7 @@ private fun computeSuggestedIntermediateTypeName(targetType: PyType?, actualType
     fun mro(t: PyClassLikeType): List<PyClassLikeType> {
       val result = ArrayList<PyClassLikeType>()
       result.add(t)
-      result.addAll(t.getAncestorTypes(context))
+      result.addAll(t.getAncestorTypes(context).filterNotNull())
       return result
     }
 
diff --git a/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyClassTypeImpl.java b/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyClassTypeImpl.java
index bd7c348945da..488873c02174 100644
--- a/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyClassTypeImpl.java
+++ b/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyClassTypeImpl.java
@@ -378,7 +378,7 @@ public class PyClassTypeImpl extends UserDataHolderBase implements PyClassType {
   }
 
   @Override
-  public @NotNull List<PyClassLikeType> getAncestorTypes(final @NotNull TypeEvalContext context) {
+  public @NotNull List<@Nullable PyClassLikeType> getAncestorTypes(final @NotNull TypeEvalContext context) {
     return myClass.getAncestorTypes(context);
   }
 
@@ -746,7 +746,7 @@ public class PyClassTypeImpl extends UserDataHolderBase implements PyClassType {
     }
   }
 
-  private @NotNull StreamEx<PyClassLikeType> prepareTypesForProcessingMembers(@NotNull List<PyClassLikeType> types) {
+  private @NotNull StreamEx<PyClassLikeType> prepareTypesForProcessingMembers(@NotNull List<@Nullable PyClassLikeType> types) {
     return StreamEx.of(types).nonNull().map(type -> isDefinition() ? type.toClass() : type.toInstance());
   }
 
diff --git a/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyTypingNewType.kt b/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyTypingNewType.kt
index 5802ea77c508..9ec4d735ea8b 100644
--- a/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyTypingNewType.kt
+++ b/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyTypingNewType.kt
@@ -77,7 +77,7 @@ class PyTypingNewType(private val classType: PyClassType,
     }
   }
 
-  override fun getAncestorTypes(context: TypeEvalContext): List<PyClassLikeType> {
+  override fun getAncestorTypes(context: TypeEvalContext): List<PyClassLikeType?> {
     return listOf(classType) + classType.getAncestorTypes(context)
   }