diff --git a/python/python-common-tests/com/jetbrains/python/PythonCommonCompletionTest.java b/python/python-common-tests/com/jetbrains/python/PythonCommonCompletionTest.java
index 0b381753fc24..7158e34ba4fc 100644
--- a/python/python-common-tests/com/jetbrains/python/PythonCommonCompletionTest.java
+++ b/python/python-common-tests/com/jetbrains/python/PythonCommonCompletionTest.java
@@ -12,6 +12,7 @@ import com.intellij.openapi.vfs.VirtualFile;
 import com.jetbrains.python.documentation.docstrings.DocStringFormat;
 import com.jetbrains.python.fixture.PythonCommonTestCase;
 import com.jetbrains.python.psi.LanguageLevel;
+import com.jetbrains.python.sdk.PythonSdkUtil;
 import one.util.streamex.StreamEx;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -1711,6 +1712,20 @@ public abstract class PythonCommonCompletionTest extends PythonCommonTestCase {
     doTestHasattrContributor(inList, null);
   }
 
+  // PY-39956
+  public void testDuplicatesFromProvider() {
+    final String testName = getTestName(true);
+
+    final VirtualFile skeletonsDir =
+      StandardFileSystems.local().findFileByPath(getTestDataPath() + "/" + testName + "/" + PythonSdkUtil.SKELETON_DIR_NAME);
+
+    assertNotNull(skeletonsDir);
+    runWithAdditionalClassEntryInSdkRoots(
+      skeletonsDir,
+      () -> assertNull(doTestByText("from itertools import prod<caret>"))
+    );
+  }
+
   private void doTestHasattrContributor(String[] inList, String[] notInList) {
     doTestHasattrContributor("hasattrCompletion/" + getTestName(true) + ".py", inList, notInList);
   }
diff --git a/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyModuleType.java b/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyModuleType.java
index c9a6d9257189..e68c453e14e5 100644
--- a/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyModuleType.java
+++ b/python/python-psi-impl/src/com/jetbrains/python/psi/types/PyModuleType.java
@@ -21,10 +21,10 @@ import com.intellij.util.containers.ContainerUtil;
 import com.jetbrains.python.PyNames;
 import com.jetbrains.python.codeInsight.PyCustomMember;
 import com.jetbrains.python.codeInsight.completion.PyCompletionUtilsKt;
-import com.jetbrains.python.codeInsight.mlcompletion.PyCompletionMlElementInfo;
-import com.jetbrains.python.codeInsight.mlcompletion.PyCompletionMlElementKind;
 import com.jetbrains.python.codeInsight.controlflow.ScopeOwner;
 import com.jetbrains.python.codeInsight.dataflow.scope.ScopeUtil;
+import com.jetbrains.python.codeInsight.mlcompletion.PyCompletionMlElementInfo;
+import com.jetbrains.python.codeInsight.mlcompletion.PyCompletionMlElementKind;
 import com.jetbrains.python.psi.*;
 import com.jetbrains.python.psi.impl.PyImportedModule;
 import com.jetbrains.python.psi.impl.ResolveResultList;
@@ -419,8 +419,8 @@ public class PyModuleType implements PyType { // Modules don't descend from obje
     for (PyModuleMembersProvider provider : PyModuleMembersProvider.EP_NAME.getExtensionList()) {
       for (PyCustomMember member : provider.getMembers(myModule, point, typeEvalContext)) {
         final String name = member.getName();
-        if (namesAlready != null) {
-          namesAlready.add(name);
+        if (namesAlready != null && !namesAlready.add(name)) {
+          continue;
         }
         if (PyUtil.isClassPrivateName(name)) {
           continue;
diff --git a/python/testData/completion/duplicatesFromProvider/python_stubs/itertools.py b/python/testData/completion/duplicatesFromProvider/python_stubs/itertools.py
new file mode 100644
index 000000000000..d7003139cdc2
--- /dev/null
+++ b/python/testData/completion/duplicatesFromProvider/python_stubs/itertools.py
@@ -0,0 +1,2 @@
+def product():
+    pass
\ No newline at end of file