diff --git a/python/psi-api/src/com/jetbrains/python/psi/PyCustomizableStubElementType.java b/python/psi-api/src/com/jetbrains/python/psi/PyCustomizableStubElementType.java
new file mode 100644
index 000000000000..a1dccab8b600
--- /dev/null
+++ b/python/psi-api/src/com/jetbrains/python/psi/PyCustomizableStubElementType.java
@@ -0,0 +1,53 @@
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.jetbrains.python.psi;
+
+import com.intellij.psi.stubs.StubInputStream;
+import com.intellij.psi.stubs.StubOutputStream;
+import com.jetbrains.python.psi.impl.stubs.PyCustomStub;
+import com.jetbrains.python.psi.impl.stubs.PyCustomStubType;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.io.IOException;
+import java.util.List;
+
+public interface PyCustomizableStubElementType<Psi extends PyElement, Stub extends PyCustomStub, StubType extends PyCustomStubType<Psi, ? extends Stub>> {
+
+  @NotNull
+  List<StubType> getExtensions();
+
+  @Nullable
+  default Stub createCustomStub(@NotNull Psi psi) {
+    for (StubType type : getExtensions()) {
+      final Stub stub = type.createStub(psi);
+      if (stub != null) return stub;
+    }
+
+    return null;
+  }
+
+  default void serializeCustomStub(@Nullable Stub stub, @NotNull StubOutputStream stream) throws IOException {
+    final boolean hasCustomStub = stub != null;
+    stream.writeBoolean(hasCustomStub);
+
+    if (hasCustomStub) {
+      stream.writeName(stub.getTypeClass().getCanonicalName());
+      stub.serialize(stream);
+    }
+  }
+
+  @Nullable
+  default Stub deserializeCustomStub(@NotNull StubInputStream stream) throws IOException {
+    if (stream.readBoolean()) {
+      final String typeName = stream.readNameString();
+      for (StubType type : getExtensions()) {
+        if (type.getClass().getCanonicalName().equals(typeName)) {
+          return type.deserializeStub(stream);
+        }
+      }
+      throw new IOException("Unknown custom stub type " + typeName);
+    }
+
+    return null;
+  }
+}
diff --git a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStub.java b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStub.java
index 5f6485b881d7..1eb66de0a8cf 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStub.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStub.java
@@ -15,20 +15,13 @@
  */
 package com.jetbrains.python.psi.impl.stubs;
 
-import com.intellij.psi.stubs.StubOutputStream;
 import com.intellij.psi.util.QualifiedName;
-import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.io.IOException;
-
 /**
  * @author yole
  */
-public interface CustomTargetExpressionStub {
-  @NotNull
-  Class<? extends CustomTargetExpressionStubType> getTypeClass();
-  void serialize(StubOutputStream stream) throws IOException;
+public interface CustomTargetExpressionStub extends PyCustomStub<CustomTargetExpressionStubType> {
 
   @Nullable
   QualifiedName getCalleeName();
diff --git a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStubType.java b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStubType.java
index 8215dc15f5a1..818b5cd30459 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStubType.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/CustomTargetExpressionStubType.java
@@ -17,24 +17,17 @@ package com.jetbrains.python.psi.impl.stubs;
 
 import com.intellij.openapi.extensions.ExtensionPointName;
 import com.intellij.psi.stubs.IndexSink;
-import com.intellij.psi.stubs.StubInputStream;
 import com.jetbrains.python.psi.PyTargetExpression;
 import com.jetbrains.python.psi.stubs.PyTargetExpressionStub;
-import org.jetbrains.annotations.Nullable;
-
-import java.io.IOException;
 
 /**
  * @author yole
  */
-public abstract class CustomTargetExpressionStubType<T extends CustomTargetExpressionStub> {
-  public static final ExtensionPointName<CustomTargetExpressionStubType> EP_NAME = ExtensionPointName.create("Pythonid.customTargetExpressionStubType");
+public abstract class CustomTargetExpressionStubType<T extends CustomTargetExpressionStub>
+  implements PyCustomStubType<PyTargetExpression, T> {
 
-  @Nullable
-  public abstract T createStub(PyTargetExpression psi);
-
-  @Nullable
-  public abstract T deserializeStub(StubInputStream stream) throws IOException;
+  public static final ExtensionPointName<CustomTargetExpressionStubType<? extends CustomTargetExpressionStub>> EP_NAME =
+    ExtensionPointName.create("Pythonid.customTargetExpressionStubType");
 
   public void indexStub(PyTargetExpressionStub stub, IndexSink sink) {
   }
diff --git a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStub.java b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStub.java
index ef1cb6c57e42..0312fd61107d 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStub.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStub.java
@@ -1,24 +1,5 @@
 // Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package com.jetbrains.python.psi.impl.stubs;
 
-import com.intellij.psi.stubs.StubInputStream;
-import com.intellij.psi.stubs.StubOutputStream;
-import org.jetbrains.annotations.NotNull;
-
-import java.io.IOException;
-
-public interface PyCustomClassStub {
-
-  /**
-   * @return type class to distinguish one custom stub from another.
-   */
-  @NotNull
-  Class<? extends PyCustomClassStubType> getTypeClass();
-
-  /**
-   * @param stream stream to serialize {@code this} stub
-   * @throws IOException
-   * @see PyCustomClassStubType#deserializeStub(StubInputStream)
-   */
-  void serialize(@NotNull StubOutputStream stream) throws IOException;
+public interface PyCustomClassStub extends PyCustomStub<PyCustomClassStubType> {
 }
diff --git a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStubType.java b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStubType.java
index 7651e3dc9225..2dcfee0d5dcb 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStubType.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomClassStubType.java
@@ -2,31 +2,10 @@
 package com.jetbrains.python.psi.impl.stubs;
 
 import com.intellij.openapi.extensions.ExtensionPointName;
-import com.intellij.psi.stubs.StubInputStream;
-import com.intellij.psi.stubs.StubOutputStream;
 import com.jetbrains.python.psi.PyClass;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 
-import java.io.IOException;
+public abstract class PyCustomClassStubType<T extends PyCustomClassStub> implements PyCustomStubType<PyClass, T> {
 
-public abstract class PyCustomClassStubType<T extends PyCustomClassStub> {
-
-  public static final ExtensionPointName<PyCustomClassStubType> EP_NAME = ExtensionPointName.create("Pythonid.customClassStubType");
-
-  /**
-   * @param psi class to create stub for
-   * @return custom stub for given class or null.
-   */
-  @Nullable
-  public abstract T createStub(@NotNull PyClass psi);
-
-  /**
-   * @param stream stream containing serialized stub
-   * @return a custom stub instance or null if it could not be read.
-   * @throws IOException
-   * @see PyCustomClassStub#serialize(StubOutputStream)
-   */
-  @Nullable
-  public abstract T deserializeStub(@NotNull StubInputStream stream) throws IOException;
+  public static final ExtensionPointName<PyCustomClassStubType<? extends PyCustomClassStub>> EP_NAME =
+    ExtensionPointName.create("Pythonid.customClassStubType");
 }
diff --git a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomStub.java b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomStub.java
new file mode 100644
index 000000000000..f6bf9e83b6e6
--- /dev/null
+++ b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomStub.java
@@ -0,0 +1,24 @@
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.jetbrains.python.psi.impl.stubs;
+
+import com.intellij.psi.stubs.StubInputStream;
+import com.intellij.psi.stubs.StubOutputStream;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.IOException;
+
+public interface PyCustomStub<CustomStubType extends PyCustomStubType> {
+
+  /**
+   * @return type class to distinguish one custom stub from another.
+   */
+  @NotNull
+  Class<? extends CustomStubType> getTypeClass();
+
+  /**
+   * @param stream stream to serialize {@code this} stub
+   * @throws IOException
+   * @see PyCustomStubType#deserializeStub(StubInputStream)
+   */
+  void serialize(@NotNull StubOutputStream stream) throws IOException;
+}
diff --git a/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomStubType.java b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomStubType.java
new file mode 100644
index 000000000000..295851e95d1e
--- /dev/null
+++ b/python/psi-api/src/com/jetbrains/python/psi/impl/stubs/PyCustomStubType.java
@@ -0,0 +1,29 @@
+// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.jetbrains.python.psi.impl.stubs;
+
+import com.intellij.psi.stubs.StubInputStream;
+import com.intellij.psi.stubs.StubOutputStream;
+import com.jetbrains.python.psi.PyElement;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.io.IOException;
+
+public interface PyCustomStubType<Psi extends PyElement, Stub extends PyCustomStub> {
+
+  /**
+   * @param psi element to create stub for
+   * @return custom stub for the given psi or null.
+   */
+  @Nullable
+  Stub createStub(@NotNull Psi psi);
+
+  /**
+   * @param stream stream containing serialized stub
+   * @return a custom stub instance or null if it could not be read.
+   * @throws IOException
+   * @see PyCustomStub#serialize(StubOutputStream)
+   */
+  @Nullable
+  Stub deserializeStub(@NotNull StubInputStream stream) throws IOException;
+}
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
index fcb14acf4a97..eba3a78da104 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
@@ -12,7 +12,6 @@ import com.jetbrains.python.psi.impl.PyClassImpl;
 import com.jetbrains.python.psi.impl.PyPsiUtils;
 import com.jetbrains.python.psi.resolve.PyResolveUtil;
 import com.jetbrains.python.psi.stubs.*;
-import one.util.streamex.StreamEx;
 import org.jetbrains.annotations.NonNls;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -25,10 +24,8 @@ import static com.jetbrains.python.psi.PyUtil.as;
 /**
  * @author max
  */
-public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass> {
-
-  @Nullable
-  private List<PyCustomClassStubType> myCustomStubTypes;
+public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
+  implements PyCustomizableStubElementType<PyClass, PyCustomClassStub, PyCustomClassStubType<? extends PyCustomClassStub>> {
 
   public PyClassElementType() {
     this("CLASS_DECLARATION");
@@ -52,12 +49,6 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
   @Override
   @NotNull
   public PyClassStub createStub(@NotNull final PyClass psi, final StubElement parentStub) {
-    final PyCustomClassStub customStub = StreamEx
-      .of(getCustomStubTypes())
-      .map(type -> type.createStub(psi))
-      .findFirst(Objects::nonNull)
-      .orElse(null);
-
     return new PyClassStubImpl(psi.getName(),
                                parentStub,
                                getSuperClassQNames(psi),
@@ -67,7 +58,7 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
                                psi.getOwnSlots(),
                                PyPsiUtils.strValue(psi.getDocStringExpression()),
                                getStubElementType(),
-                               customStub);
+                               createCustomStub(psi));
   }
 
   @NotNull
@@ -160,19 +151,7 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
     final String docString = pyClassStub.getDocString();
     dataStream.writeUTFFast(docString != null ? docString : "");
 
-    serializeCustomStub(pyClassStub, dataStream);
-  }
-
-  private static void serializeCustomStub(@NotNull PyClassStub stub, @NotNull StubOutputStream stream) throws IOException {
-    final PyCustomClassStub customStub = stub.getCustomStub(PyCustomClassStub.class);
-
-    final boolean hasCustomStub = customStub != null;
-    stream.writeBoolean(hasCustomStub);
-
-    if (hasCustomStub) {
-      stream.writeName(customStub.getTypeClass().getCanonicalName());
-      customStub.serialize(stream);
-    }
+    serializeCustomStub(pyClassStub.getCustomStub(PyCustomClassStub.class), dataStream);
   }
 
   @Override
@@ -212,21 +191,6 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
                                getStubElementType(), customStub);
   }
 
-  @Nullable
-  private PyCustomClassStub deserializeCustomStub(@NotNull StubInputStream stream) throws IOException {
-    if (stream.readBoolean()) {
-      final String typeName = stream.readNameString();
-      for (PyCustomClassStubType type : getCustomStubTypes()) {
-        if (type.getClass().getCanonicalName().equals(typeName)) {
-          return type.deserializeStub(stream);
-        }
-      }
-      throw new IOException("Unknown custom class stub type " + typeName);
-    }
-
-    return null;
-  }
-
   @Override
   public void indexStub(@NotNull final PyClassStub stub, @NotNull final IndexSink sink) {
     final String name = stub.getName();
@@ -253,10 +217,8 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
   }
 
   @NotNull
-  private List<PyCustomClassStubType> getCustomStubTypes() {
-    if (myCustomStubTypes == null) {
-      myCustomStubTypes = PyCustomClassStubType.EP_NAME.getExtensionList();
-    }
-    return myCustomStubTypes;
+  @Override
+  public List<PyCustomClassStubType<? extends PyCustomClassStub>> getExtensions() {
+    return PyCustomClassStubType.EP_NAME.getExtensionList();
   }
 }
\ No newline at end of file
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java b/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java
index 3fd49ef02d75..d9366c5bd8e7 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyTargetExpressionElementType.java
@@ -28,8 +28,9 @@ import java.util.List;
 /**
  * @author yole
  */
-public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExpressionStub, PyTargetExpression> {
-  private List<CustomTargetExpressionStubType> myCustomStubTypes;
+public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExpressionStub, PyTargetExpression>
+  implements
+  PyCustomizableStubElementType<PyTargetExpression, CustomTargetExpressionStub, CustomTargetExpressionStubType<? extends CustomTargetExpressionStub>> {
 
   public PyTargetExpressionElementType() {
     super("TARGET_EXPRESSION");
@@ -39,13 +40,6 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
     super(debugName);
   }
 
-  private List<CustomTargetExpressionStubType> getCustomStubTypes() {
-    if (myCustomStubTypes == null) {
-      myCustomStubTypes = CustomTargetExpressionStubType.EP_NAME.getExtensionList();
-    }
-    return myCustomStubTypes;
-  }
-
   @Override
   @NotNull
   public PsiElement createElement(@NotNull final ASTNode node) {
@@ -66,12 +60,11 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
     final String typeComment = psi.getTypeCommentAnnotation();
     final String annotation = psi.getAnnotationValue();
 
-    for (CustomTargetExpressionStubType customStubType : getCustomStubTypes()) {
-      CustomTargetExpressionStub customStub = customStubType.createStub(psi);
-      if (customStub != null) {
-        return new PyTargetExpressionStubImpl(name, docString, typeComment, annotation, psi.hasAssignedValue(), customStub, parentStub);
-      }
+    CustomTargetExpressionStub customStub = createCustomStub(psi);
+    if (customStub != null) {
+      return new PyTargetExpressionStubImpl(name, docString, typeComment, annotation, psi.hasAssignedValue(), customStub, parentStub);
     }
+
     PyTargetExpressionStub.InitializerType initializerType = PyTargetExpressionStub.InitializerType.Other;
     QualifiedName initializer = null;
     if (assignedValue instanceof PyReferenceExpression) {
@@ -100,8 +93,7 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
     stream.writeBoolean(stub.hasAssignedValue());
     final CustomTargetExpressionStub customStub = stub.getCustomStub(CustomTargetExpressionStub.class);
     if (customStub != null) {
-      stream.writeName(customStub.getTypeClass().getCanonicalName());
-      customStub.serialize(stream);
+      serializeCustomStub(customStub, stream);
     }
     else {
       QualifiedName.serialize(stub.getInitializer(), stream);
@@ -122,14 +114,8 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
     String annotation = stream.readNameString();
     final boolean hasAssignedValue = stream.readBoolean();
     if (initializerType == PyTargetExpressionStub.InitializerType.Custom) {
-      final String typeName = stream.readNameString();
-      for(CustomTargetExpressionStubType type: getCustomStubTypes()) {
-        if (type.getClass().getCanonicalName().equals(typeName)) {
-          CustomTargetExpressionStub stub = type.deserializeStub(stream);
-          return new PyTargetExpressionStubImpl(name, docString, typeComment, annotation, hasAssignedValue, stub, parentStub);
-        }
-      }
-      throw new IOException("Unknown custom stub type " + typeName);
+      CustomTargetExpressionStub stub = deserializeCustomStub(stream);
+      return new PyTargetExpressionStubImpl(name, docString, typeComment, annotation, hasAssignedValue, stub, parentStub);
     }
     QualifiedName initializer = QualifiedName.deserialize(stream);
     boolean isQualified = stream.readBoolean();
@@ -167,8 +153,14 @@ public class PyTargetExpressionElementType extends PyStubElementType<PyTargetExp
         sink.occurrence(PyVariableNameIndex.KEY, name);
       }
     }
-    for (CustomTargetExpressionStubType stubType : getCustomStubTypes()) {
+    for (CustomTargetExpressionStubType stubType : getExtensions()) {
       stubType.indexStub(stub, sink);
     }
   }
+
+  @NotNull
+  @Override
+  public List<CustomTargetExpressionStubType<? extends CustomTargetExpressionStub>> getExtensions() {
+    return CustomTargetExpressionStubType.EP_NAME.getExtensionList();
+  }
 }
diff --git a/python/src/com/jetbrains/python/psi/impl/stubs/PyTypingNewTypeStubType.kt b/python/src/com/jetbrains/python/psi/impl/stubs/PyTypingNewTypeStubType.kt
index bcb41e33bfa7..5469b3cf9b96 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyTypingNewTypeStubType.kt
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyTypingNewTypeStubType.kt
@@ -8,12 +8,11 @@ import com.jetbrains.python.psi.stubs.PyTypingNewTypeStub
 
 class PyTypingNewTypeStubType : CustomTargetExpressionStubType<PyTypingNewTypeStub>() {
 
-  override fun createStub(psi: PyTargetExpression?): PyTypingNewTypeStub? {
+  override fun createStub(psi: PyTargetExpression): PyTypingNewTypeStub? {
     return PyTypingNewTypeStubImpl.create(psi)
   }
 
-  override fun deserializeStub(stream: StubInputStream?): PyTypingNewTypeStub? {
+  override fun deserializeStub(stream: StubInputStream): PyTypingNewTypeStub? {
     return PyTypingNewTypeStubImpl.deserialize(stream)
   }
-
 }
\ No newline at end of file