diff --git a/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/ArchiveContainerInfo.java b/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/ArchiveContainerInfo.java
index bd79fed2ed7..23788a58cc5 100644
--- a/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/ArchiveContainerInfo.java
+++ b/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/ArchiveContainerInfo.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2008 QNX Software Systems and others.
+ * Copyright (c) 2000, 2021 QNX Software Systems and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -36,8 +36,6 @@ public class ArchiveContainerInfo extends OpenableInfo {
 
 	@Override
 	protected void addChild(ICElement child) {
-		if (!includesChild(child)) {
-			super.addChild(child);
-		}
+		addChildIfAbsent(child);
 	}
 }
diff --git a/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/BinaryContainerInfo.java b/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/BinaryContainerInfo.java
index 07340c2d67c..4196d3a8db3 100644
--- a/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/BinaryContainerInfo.java
+++ b/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/BinaryContainerInfo.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2008 QNX Software Systems and others.
+ * Copyright (c) 2000, 2021 QNX Software Systems and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -29,8 +29,6 @@ public class BinaryContainerInfo extends OpenableInfo {
 
 	@Override
 	protected void addChild(ICElement child) {
-		if (!includesChild(child)) {
-			super.addChild(child);
-		}
+		addChildIfAbsent(child);
 	}
 }
diff --git a/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/CElementInfo.java b/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/CElementInfo.java
index 8e0e70f69e0..88a44167a80 100644
--- a/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/CElementInfo.java
+++ b/core/org.eclipse.cdt.core/model/org/eclipse/cdt/internal/core/model/CElementInfo.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2009 QNX Software Systems and others.
+ * Copyright (c) 2000, 2021 QNX Software Systems and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -64,6 +64,14 @@ public class CElementInfo {
 		fChildren.add(child);
 	}
 
+	protected void addChildIfAbsent(ICElement child) {
+		synchronized (fChildren) {
+			if (!fChildren.contains(child)) {
+				fChildren.add(child);
+			}
+		}
+	}
+
 	protected ICElement[] getChildren() {
 		synchronized (fChildren) {
 			ICElement[] array = new ICElement[fChildren.size()];