diff --git a/maven-core/src/main/java/org/apache/maven/DefaultMaven.java b/maven-core/src/main/java/org/apache/maven/DefaultMaven.java
index e1880ecae4..c610798ba1 100644
--- a/maven-core/src/main/java/org/apache/maven/DefaultMaven.java
+++ b/maven-core/src/main/java/org/apache/maven/DefaultMaven.java
@@ -339,7 +339,7 @@ public class DefaultMaven implements Maven {
     private void setupWorkspaceReader(MavenSession session, DefaultRepositorySystemSession repoSession)
             throws ComponentLookupException {
         // Desired order of precedence for workspace readers before querying the local artifact repositories
-        List<WorkspaceReader> workspaceReaders = new ArrayList<>();
+        Set<WorkspaceReader> workspaceReaders = new LinkedHashSet<>();
         // 1) Reactor workspace reader
         WorkspaceReader reactorReader = container.lookup(WorkspaceReader.class, ReactorReader.HINT);
         workspaceReaders.add(reactorReader);
@@ -349,13 +349,7 @@ public class DefaultMaven implements Maven {
             workspaceReaders.add(repoWorkspaceReader);
         }
         // 3) .. n) Project-scoped workspace readers
-        for (WorkspaceReader workspaceReader :
-                getProjectScopedExtensionComponents(session.getProjects(), WorkspaceReader.class)) {
-            if (workspaceReaders.contains(workspaceReader)) {
-                continue;
-            }
-            workspaceReaders.add(workspaceReader);
-        }
+        workspaceReaders.addAll(getProjectScopedExtensionComponents(session.getProjects(), WorkspaceReader.class));
         repoSession.setWorkspaceReader(MavenChainedWorkspaceReader.of(workspaceReaders));
     }
 
diff --git a/maven-core/src/main/java/org/apache/maven/ReactorReader.java b/maven-core/src/main/java/org/apache/maven/ReactorReader.java
index 900b5d575a..a4b2a4c868 100644
--- a/maven-core/src/main/java/org/apache/maven/ReactorReader.java
+++ b/maven-core/src/main/java/org/apache/maven/ReactorReader.java
@@ -35,6 +35,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Deque;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -69,8 +70,8 @@ class ReactorReader implements MavenWorkspaceReader {
 
     public static final String PROJECT_LOCAL_REPO = "project-local-repo";
 
-    private static final Collection<String> COMPILE_PHASE_TYPES =
-            Arrays.asList("jar", "ejb-client", "war", "rar", "ejb3", "par", "sar", "wsr", "har", "app-client");
+    private static final Collection<String> COMPILE_PHASE_TYPES = new HashSet<>(
+            Arrays.asList("jar", "ejb-client", "war", "rar", "ejb3", "par", "sar", "wsr", "har", "app-client"));
 
     private static final Logger LOGGER = LoggerFactory.getLogger(ReactorReader.class);