diff --git a/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java b/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java
index 8a6b92d87cdf..e567f497ca00 100644
--- a/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java
+++ b/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java
@@ -67,15 +67,13 @@ public class PyFileImpl extends PsiFileBase implements PyFile, PyExpression {
     private ExportedNameCache(long modificationStamp) {
       myModificationStamp = modificationStamp;
 
-      processDeclarations(PyPsiUtils.collectAllStubChildren(PyFileImpl.this, getStub()), element -> {
-        if (element instanceof PsiNamedElement && !(element instanceof PyKeywordArgument)) {
+      final StubElement stub = getStub();
+      processDeclarations(PyPsiUtils.collectAllStubChildren(PyFileImpl.this, stub), element -> {
+        if (element instanceof PsiNamedElement &&
+            !(element instanceof PyKeywordArgument) &&
+            !(stub == null && element.getParent() instanceof PyImportElement)) {
           final PsiNamedElement namedElement = (PsiNamedElement)element;
-          final String name = namedElement.getName();
-          if (!myNamedElements.containsKey(name)) {
-            myNamedElements.put(name, Lists.newArrayList());
-          }
-          final List<PsiNamedElement> elements = myNamedElements.get(name);
-          elements.add(namedElement);
+          myNamedElements.computeIfAbsent(namedElement.getName(), __ -> new ArrayList<>()).add(namedElement);
         }
         if (element instanceof PyImportedNameDefiner) {
           myImportedNameDefiners.add((PyImportedNameDefiner)element);
@@ -758,13 +756,6 @@ public class PyFileImpl extends PsiFileBase implements PyFile, PyExpression {
     return newElement;
   }
 
-  private static class ArrayListThreadLocal extends ThreadLocal<List<String>> {
-    @Override
-    protected List<String> initialValue() {
-      return new ArrayList<>();
-    }
-  }
-
   @Override
   public ItemPresentation getPresentation() {
     return new ItemPresentation() {
diff --git a/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/A.py b/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/A.py
new file mode 100644
index 000000000000..25fc6b72ad0b
--- /dev/null
+++ b/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/A.py
@@ -0,0 +1,3 @@
+class A(object):
+    def __init__(self, x):  # <- Has argument x
+        self.x = x
diff --git a/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/BC.py b/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/BC.py
new file mode 100644
index 000000000000..9675f4d71dfa
--- /dev/null
+++ b/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/BC.py
@@ -0,0 +1,9 @@
+from A import A as myA  # No problem without the 'as'
+
+
+class B(object):
+    pass
+
+
+class C(myA, B):  # No problem when only inheriting from myA
+    pass
diff --git a/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/D.py b/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/D.py
new file mode 100644
index 000000000000..413b0860b3e7
--- /dev/null
+++ b/python/testData/codeInsight/classMRO/ClassImportedFromUnstubbedFileAndSuperImportedWithAs/D.py
@@ -0,0 +1,10 @@
+from BC import C  # No problem if D is also in BC.py
+
+
+class D(C):
+    def __init__(self, x):
+        C.__init__(self, x)  # <- "Unexpected argument" warning for x
+
+
+d = D(4)
+assert d.x == 4  # runs fine
diff --git a/python/testSrc/com/jetbrains/python/codeInsight/PyClassMROTest.java b/python/testSrc/com/jetbrains/python/codeInsight/PyClassMROTest.java
index 45dcd0f709b3..e93969dffc4b 100644
--- a/python/testSrc/com/jetbrains/python/codeInsight/PyClassMROTest.java
+++ b/python/testSrc/com/jetbrains/python/codeInsight/PyClassMROTest.java
@@ -15,10 +15,15 @@
  */
 package com.jetbrains.python.codeInsight;
 
+import com.intellij.openapi.vfs.VirtualFile;
+import com.intellij.psi.PsiFile;
 import com.intellij.util.ArrayUtil;
+import com.intellij.util.containers.ContainerUtil;
+import com.jetbrains.python.PyNames;
 import com.jetbrains.python.fixtures.PyTestCase;
 import com.jetbrains.python.psi.LanguageLevel;
 import com.jetbrains.python.psi.PyClass;
+import com.jetbrains.python.psi.PyFile;
 import com.jetbrains.python.psi.types.PyClassLikeType;
 import com.jetbrains.python.psi.types.PyClassType;
 import com.jetbrains.python.psi.types.PyType;
@@ -162,8 +167,28 @@ public class PyClassMROTest extends PyTestCase {
     });
   }
 
+  // PY-21837
+  public void testClassImportedFromUnstubbedFileAndSuperImportedWithAs() {
+    myFixture.copyDirectoryToProject("codeInsight/classMRO/" + getTestName(false), "");
+
+    final VirtualFile d = myFixture.findFileInTempDir("D.py");
+    final VirtualFile bc = myFixture.findFileInTempDir("BC.py");
+
+    final PyFile dPsi = (PyFile)myFixture.getPsiManager().findFile(d);
+    final PsiFile bPsi = myFixture.getPsiManager().findFile(bc);
+
+    //noinspection ResultOfMethodCallIgnored
+    bPsi.getNode(); // unstubbing is necessary
+
+    final PyClass dClass = dPsi.findTopLevelClass("D");
+    final TypeEvalContext context = TypeEvalContext.codeAnalysis(myFixture.getProject(), dPsi); // such context is necessary
+    final List<PyClass> ancestors = dClass.getAncestorClasses(context);
+
+    assertOrderedEquals(ContainerUtil.map(ancestors, PyClass::getName), Arrays.asList("C", "A", "B", PyNames.OBJECT));
+  }
+
   @NotNull
-  public PyClass getClass(@NotNull String name) {
+  private PyClass getClass(@NotNull String name) {
     myFixture.configureByFile(getPath(getTestName(false)));
     final PyClass cls = myFixture.findElementByText(name, PyClass.class);
     assertNotNull(cls);