diff --git a/python/psi-api/src/com/jetbrains/python/PyNames.java b/python/psi-api/src/com/jetbrains/python/PyNames.java
index da970ed07576..e1b99d0135a8 100644
--- a/python/psi-api/src/com/jetbrains/python/PyNames.java
+++ b/python/psi-api/src/com/jetbrains/python/PyNames.java
@@ -65,6 +65,7 @@ public class PyNames {
   public static final String ASSERT_IS_INSTANCE = "assertIsInstance";
   public static final String HAS_ATTR = "hasattr";
 
+  public static final String DOC = "__doc__";
   public static final String DOCFORMAT = "__docformat__";
 
   public static final String DIRNAME = "dirname";
diff --git a/python/psi-api/src/com/jetbrains/python/psi/PyAssignmentStatement.java b/python/psi-api/src/com/jetbrains/python/psi/PyAssignmentStatement.java
index 4a6977bc82b1..2490ba4a24b0 100644
--- a/python/psi-api/src/com/jetbrains/python/psi/PyAssignmentStatement.java
+++ b/python/psi-api/src/com/jetbrains/python/psi/PyAssignmentStatement.java
@@ -62,4 +62,6 @@ public interface PyAssignmentStatement extends PyStatement, NameDefiner {
   @Nullable
   PyExpression getLeftHandSideExpression();
 
+  boolean isAssignmentTo(@NotNull String name);
+
 }
diff --git a/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java b/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java
index d46826399c8d..57a7fef14bb4 100644
--- a/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java
+++ b/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java
@@ -139,6 +139,12 @@ public class PyAssignmentStatementImpl extends PyElementImpl implements PyAssign
     return (PyExpression)child;
   }
 
+  @Override
+  public boolean isAssignmentTo(@NotNull String name) {
+    PyExpression lhs = getLeftHandSideExpression();
+    return lhs instanceof PyTargetExpression && name.equals(lhs.getName());
+  }
+
   private static void mapToValues(PyExpression lhs, PyExpression rhs, List<Pair<PyExpression, PyExpression>> map) {
     // cast for convenience
     PySequenceExpression lhs_tuple = null;
diff --git a/python/src/com/jetbrains/python/validation/DocStringAnnotator.java b/python/src/com/jetbrains/python/validation/DocStringAnnotator.java
index 51ceb1aef815..76b5c2df8dd6 100644
--- a/python/src/com/jetbrains/python/validation/DocStringAnnotator.java
+++ b/python/src/com/jetbrains/python/validation/DocStringAnnotator.java
@@ -4,6 +4,7 @@ import com.intellij.lang.annotation.Annotation;
 import com.intellij.openapi.module.Module;
 import com.intellij.openapi.module.ModuleUtilCore;
 import com.intellij.openapi.util.TextRange;
+import com.jetbrains.python.PyNames;
 import com.jetbrains.python.documentation.*;
 import com.jetbrains.python.highlighting.PyHighlighter;
 import com.jetbrains.python.psi.*;
@@ -30,8 +31,7 @@ public class DocStringAnnotator extends PyAnnotator {
 
   @Override
   public void visitPyAssignmentStatement(PyAssignmentStatement node) {
-    PyExpression left = node.getLeftHandSideExpression();
-    if (left != null && "__doc__".equals(left.getName())) {
+    if (node.isAssignmentTo(PyNames.DOC)) {
       PyExpression right = node.getAssignedValue();
       if (right instanceof PyStringLiteralExpression) {
         Annotation ann = getHolder().createInfoAnnotation(right, null);