diff --git a/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProvider.java b/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProvider.java
index 672b37fffd0b..16f0dce67a89 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProvider.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProvider.java
@@ -3,6 +3,7 @@ package com.jetbrains.python.psi.types;
 import com.intellij.openapi.extensions.ExtensionPointName;
 import com.intellij.psi.PsiElement;
 import com.jetbrains.python.codeInsight.PyDynamicMember;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
@@ -13,6 +14,7 @@ import java.util.Collection;
 public interface PyClassMembersProvider {
   ExtensionPointName<PyClassMembersProvider> EP_NAME = ExtensionPointName.create("Pythonid.pyClassMembersProvider");
 
+  @NotNull
   Collection<PyDynamicMember> getMembers(PyClassType clazz, @Nullable PsiElement location);
 
   @Nullable
diff --git a/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProviderBase.java b/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProviderBase.java
index ef91d4ef8ddb..3eb2ef1e11b3 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProviderBase.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/types/PyClassMembersProviderBase.java
@@ -3,6 +3,7 @@ package com.jetbrains.python.psi.types;
 import com.intellij.psi.PsiElement;
 import com.jetbrains.python.codeInsight.PyDynamicMember;
 import com.jetbrains.python.psi.PyClass;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
@@ -12,6 +13,7 @@ import java.util.Collections;
  * @author yole
  */
 public class PyClassMembersProviderBase implements PyClassMembersProvider {
+  @NotNull
   @Override
   public Collection<PyDynamicMember> getMembers(PyClassType clazz, PsiElement location) {
     return Collections.emptyList();
diff --git a/python/src/com/jetbrains/python/codeInsight/stdlib/PyStdlibClassMembersProvider.java b/python/src/com/jetbrains/python/codeInsight/stdlib/PyStdlibClassMembersProvider.java
index 231ea319bb1d..b79b07842c3d 100644
--- a/python/src/com/jetbrains/python/codeInsight/stdlib/PyStdlibClassMembersProvider.java
+++ b/python/src/com/jetbrains/python/codeInsight/stdlib/PyStdlibClassMembersProvider.java
@@ -9,6 +9,7 @@ import com.jetbrains.python.psi.PyTargetExpression;
 import com.jetbrains.python.psi.PyUtil;
 import com.jetbrains.python.psi.types.PyClassMembersProviderBase;
 import com.jetbrains.python.psi.types.PyClassType;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -21,6 +22,7 @@ import java.util.List;
 public class PyStdlibClassMembersProvider extends PyClassMembersProviderBase {
   private Key<List<PyDynamicMember>> mySocketMembersKey = Key.create("socket.members");
 
+  @NotNull
   @Override
   public Collection<PyDynamicMember> getMembers(PyClassType classType, PsiElement location) {
     PyClass clazz = classType.getPyClass();