diff --git a/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/AbstractDependencyManager.java b/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/AbstractDependencyManager.java
index 90bb3c1eb..ddba34f5d 100644
--- a/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/AbstractDependencyManager.java
+++ b/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/AbstractDependencyManager.java
@@ -185,7 +185,7 @@ public DependencyManager deriveChildManager(DependencyCollectionContext context)
             Collection<Exclusion> exclusions = managedDependency.getExclusions();
             if (!exclusions.isEmpty()) {
                 if (managedExclusions == this.managedExclusions) {
-                    managedExclusions = MMap.copy(this.managedExclusions);
+                    managedExclusions = MMap.copyWithListValue(this.managedExclusions);
                 }
                 Collection<Holder<Collection<Exclusion>>> managed = managedExclusions.get(key);
                 if (managed == null) {
diff --git a/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/MMap.java b/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/MMap.java
index af7aa34cf..3b2825015 100644
--- a/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/MMap.java
+++ b/maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/manager/MMap.java
@@ -18,7 +18,10 @@
  */
 package org.eclipse.aether.util.graph.manager;
 
+import java.util.ArrayList;
+import java.util.Collection;
 import java.util.HashMap;
+import java.util.Map;
 
 /**
  * Warning: this is a special map-like construct that suits only and should be used only in this package!
@@ -47,6 +50,15 @@ public static <K, V> MMap<K, V> copy(MMap<K, V> orig) {
         return new MMap<>(new HashMap<>(orig.delegate));
     }
 
+    public static <K, V> MMap<K, Collection<V>> copyWithListValue(MMap<K, Collection<V>> orig) {
+        HashMap<K, Collection<V>> delegateLocal = orig.delegate;
+        HashMap<K, Collection<V>> newMap = new HashMap<>((int) Math.ceil(delegateLocal.size() / 0.75D));
+        for (Map.Entry<K, Collection<V>> entry : delegateLocal.entrySet()) {
+            newMap.put(entry.getKey(), entry.getValue() == null ? null : new ArrayList<>(entry.getValue()));
+        }
+        return new MMap<>(newMap);
+    }
+
     protected final HashMap<K, V> delegate;
 
     private MMap(HashMap<K, V> delegate) {