diff --git a/python/psi-api/src/com/jetbrains/python/psi/PyClass.java b/python/psi-api/src/com/jetbrains/python/psi/PyClass.java
index 80ac706fa490..c24871db9f6d 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/PyClass.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/PyClass.java
@@ -181,6 +181,12 @@ public interface PyClass extends PsiNameIdentifierOwner, PyStatement, NameDefine
 
   boolean isSubclass(@NotNull String superClassQName);
 
+  /**
+   * Returns the aggregated list of names defined in __slots__ attributes of the class and its ancestors.
+   */
+  @Nullable
+  List<String> getSlots();
+
   /**
    * Returns the list of names in the class' __slots__ attribute, or null if the class
    * does not define such an attribute.
@@ -188,7 +194,7 @@ public interface PyClass extends PsiNameIdentifierOwner, PyStatement, NameDefine
    * @return the list of names or null.
    */
   @Nullable
-  List<String> getSlots();
+  List<String> getOwnSlots();
 
   @Nullable
   String getDocStringValue();
diff --git a/python/src/com/jetbrains/python/inspections/PyUnresolvedReferencesInspection.java b/python/src/com/jetbrains/python/inspections/PyUnresolvedReferencesInspection.java
index 4f7c75af671d..a3c9ba7d5127 100644
--- a/python/src/com/jetbrains/python/inspections/PyUnresolvedReferencesInspection.java
+++ b/python/src/com/jetbrains/python/inspections/PyUnresolvedReferencesInspection.java
@@ -128,6 +128,9 @@ public class PyUnresolvedReferencesInspection extends PyInspection {
         if (type instanceof PyClassType) {
           final PyClass pyClass = ((PyClassType)type).getPyClass();
           if (pyClass.isNewStyleClass()) {
+            if (pyClass.getOwnSlots() == null) {
+              return;
+            }
             final List<String> slots = pyClass.getSlots();
             final String attrName = node.getReferencedName();
             if (slots != null && !slots.contains(attrName) && !slots.contains(PyNames.DICT)) {
diff --git a/python/src/com/jetbrains/python/psi/impl/PyClassImpl.java b/python/src/com/jetbrains/python/psi/impl/PyClassImpl.java
index a8e506f39301..89ea4d51e1d2 100644
--- a/python/src/com/jetbrains/python/psi/impl/PyClassImpl.java
+++ b/python/src/com/jetbrains/python/psi/impl/PyClassImpl.java
@@ -246,20 +246,25 @@ public class PyClassImpl extends PyPresentableElementImpl<PyClassStub> implement
 
   @Override
   public List<String> getSlots() {
-    List<String> slots = getOwnSlots();
-    if (slots != null) {
-      return slots;
+    final Set<String> result = new LinkedHashSet<String>();
+    boolean found = false;
+    final List<String> ownSlots = getOwnSlots();
+    if (ownSlots != null) {
+      found = true;
+      result.addAll(ownSlots);
     }
     for (PyClass cls : getAncestorClasses()) {
-      slots = ((PyClassImpl)cls).getOwnSlots();
-      if (slots != null) {
-        return slots;
+      final List<String> ancestorSlots = cls.getOwnSlots();
+      if (ancestorSlots != null) {
+        found = true;
+        result.addAll(ancestorSlots);
       }
     }
-    return null;
+    return found ? new ArrayList<String>(result) : null;
   }
 
   @Nullable
+  @Override
   public List<String> getOwnSlots() {
     final PyClassStub stub = getStub();
     if (stub != null) {
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 5b584b2d2822..e0d93eb86f5f 100644
--- a/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
+++ b/python/src/com/jetbrains/python/psi/impl/stubs/PyClassElementType.java
@@ -49,7 +49,7 @@ public class PyClassElementType extends PyStubElementType<PyClassStub, PyClass>
     final PyStringLiteralExpression docStringExpression = psi.getDocStringExpression();
     return new PyClassStubImpl(psi.getName(), parentStub,
                                superClasses.toArray(new PyQualifiedName[superClasses.size()]),
-                               ((PyClassImpl)psi).getOwnSlots(),
+                               psi.getOwnSlots(),
                                PyPsiUtils.strValue(docStringExpression),
                                getStubElementType());
   }
diff --git a/python/testData/inspections/PyUnresolvedReferencesInspection/slots.py b/python/testData/inspections/PyUnresolvedReferencesInspection/slots.py
index 6929ebccd548..793903c2338b 100644
--- a/python/testData/inspections/PyUnresolvedReferencesInspection/slots.py
+++ b/python/testData/inspections/PyUnresolvedReferencesInspection/slots.py
@@ -8,7 +8,7 @@ class C(B):
     pass
 
 c = C()
-c.<warning descr="'C' object has no attribute 'bar'">bar</warning> = 1
+c.bar = 1
 
 def test_slots_with_dict():
     class C(object):