diff --git a/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java b/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java
index 1fa8b886c6d6..dbb7ec3902e0 100644
--- a/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java
+++ b/python/src/com/jetbrains/python/psi/impl/PyFileImpl.java
@@ -23,7 +23,6 @@ import com.intellij.lang.Language;
 import com.intellij.navigation.ItemPresentation;
 import com.intellij.openapi.fileTypes.FileType;
 import com.intellij.openapi.roots.ProjectFileIndex;
-import com.intellij.openapi.util.Computable;
 import com.intellij.openapi.util.Key;
 import com.intellij.openapi.util.RecursionManager;
 import com.intellij.openapi.util.io.FileUtil;
@@ -575,7 +574,24 @@ public class PyFileImpl extends PsiFileBase implements PyFile, PyExpression {
       if (callee instanceof PyQualifiedExpression) {
         final PyExpression qualifier = ((PyQualifiedExpression)callee).getQualifier();
         if (qualifier != null && PyNames.ALL.equals(qualifier.getText())) {
-          // TODO handle append and extend with constant arguments here
+          final String calleeName = callee.getName();
+          if ("append".equals(calleeName)) {
+            final PyStringLiteralExpression argument = node.getArgument(0, PyStringLiteralExpression.class);
+            if (argument != null) {
+              myResult.add(argument.getStringValue());
+              return;
+            }
+          }
+          else if ("extend".equals(calleeName)) {
+            final PyExpression argument = node.getArgument(0, PyExpression.class);
+            if (argument != null) {
+              final List<String> results = PyUtil.strListValue(argument);
+              if (results != null) {
+                myResult.addAll(results);
+                return;
+              }
+            }
+          }
           myDynamic = true;
         }
       }
diff --git a/python/testData/resolve/multiFile/dontResolveToMissingNameInDynamicDunderAll/DontResolveToMissingNameInDynamicDunderAll.py b/python/testData/resolve/multiFile/dontResolveToMissingNameInDynamicDunderAll/DontResolveToMissingNameInDynamicDunderAll.py
new file mode 100644
index 000000000000..e6ed3a8fc889
--- /dev/null
+++ b/python/testData/resolve/multiFile/dontResolveToMissingNameInDynamicDunderAll/DontResolveToMissingNameInDynamicDunderAll.py
@@ -0,0 +1,5 @@
+from m1 import *
+
+
+print(internal_name)
+#     <ref>
diff --git a/python/testData/resolve/multiFile/dontResolveToMissingNameInDynamicDunderAll/m1.py b/python/testData/resolve/multiFile/dontResolveToMissingNameInDynamicDunderAll/m1.py
new file mode 100644
index 000000000000..7d79d318040b
--- /dev/null
+++ b/python/testData/resolve/multiFile/dontResolveToMissingNameInDynamicDunderAll/m1.py
@@ -0,0 +1,13 @@
+__all__ = [
+    'foo',
+    'bar'
+]
+
+foo = 0
+bar = 1
+
+__all__.append('quux')
+
+quux = 3
+internal_name = 4
+
diff --git a/python/testSrc/com/jetbrains/python/PyMultiFileResolveTest.java b/python/testSrc/com/jetbrains/python/PyMultiFileResolveTest.java
index 6d61dfaed139..13a1f32bf97f 100644
--- a/python/testSrc/com/jetbrains/python/PyMultiFileResolveTest.java
+++ b/python/testSrc/com/jetbrains/python/PyMultiFileResolveTest.java
@@ -473,6 +473,11 @@ public class PyMultiFileResolveTest extends PyMultiFileResolveTestCase {
     assertSameElements(doMultiResolveAndGetFileUrls("pkg/__init__.py"), "pkg/mod.py");
   }
 
+  // PY-21088
+  public void testDontResolveToMissingNameInDynamicDunderAll() {
+    assertNull(doResolve());
+  }
+
   @NotNull
   private List<String> doMultiResolveAndGetFileUrls(@NotNull String currentFilePath) {
     myFixture.configureByFile(currentFilePath);