diff --git a/autotests/kcombobox_unittest.cpp b/autotests/kcombobox_unittest.cpp
--- a/autotests/kcombobox_unittest.cpp
+++ b/autotests/kcombobox_unittest.cpp
@@ -132,6 +132,21 @@
         delete testCombo; // not needed anymore
     }
 
+    void testLineEditCompletion()
+    {
+        // Test for KCombo's KLineEdit inheriting the completion object of the parent
+        KTestComboBox testCombo(false, nullptr);
+        QVERIFY(!testCombo.lineEdit());
+        auto completion = testCombo.completionObject();
+        QVERIFY(completion);
+        testCombo.setEditable(true);
+        auto lineEdit = qobject_cast<KLineEdit*>(testCombo.lineEdit());
+        QVERIFY(lineEdit);
+        QVERIFY(lineEdit->compObj());
+        QCOMPARE(lineEdit->compObj(), completion);
+        QCOMPARE(testCombo.completionObject(), completion);
+    }
+
     void testSelectionResetOnReturn()
     {
         // void QComboBoxPrivate::_q_returnPressed() calls lineEdit->deselect()
diff --git a/src/kcombobox.cpp b/src/kcombobox.cpp
--- a/src/kcombobox.cpp
+++ b/src/kcombobox.cpp
@@ -311,10 +311,17 @@
         edit = kedit;
     }
 
+    // reuse an existing completion object, if it was configured already
+    auto completion = compObj();
+
     QComboBox::setLineEdit(edit);
     d->klineEdit = qobject_cast<KLineEdit *>(edit);
     setDelegate(d->klineEdit);
 
+    if (completion && d->klineEdit) {
+        d->klineEdit->setCompletionObject(completion);
+    }
+
     // Connect the returnPressed signal for both Q[K]LineEdits'
     if (edit) {
         connect(edit, SIGNAL(returnPressed()), SIGNAL(returnPressed()));