diff --git a/maven-model-builder/pom.xml b/maven-model-builder/pom.xml
index f98c7e019fc..be93a2a485e 100644
--- a/maven-model-builder/pom.xml
+++ b/maven-model-builder/pom.xml
@@ -179,6 +179,7 @@ under the License.
               <exclude>org.apache.maven.model.superpom.SuperPomProvider#getSuperModel(java.lang.String):METHOD_RETURN_TYPE_CHANGED</exclude>
               <exclude>org.apache.maven.model.validation.DefaultModelValidator#validateDependencyVersion(org.apache.maven.model.building.ModelProblemCollector,org.apache.maven.model.Dependency,java.lang.String):METHOD_REMOVED</exclude>
               <exclude>org.apache.maven.model.validation.ModelValidator#validateFileModel(org.apache.maven.model.Model,org.apache.maven.model.building.ModelBuildingRequest,org.apache.maven.model.building.ModelProblemCollector):METHOD_NEW_DEFAULT</exclude>
+              <exclude>org.apache.maven.model.validation.ModelValidator#validateExternalProfiles(java.util.List,org.apache.maven.model.Model,org.apache.maven.model.building.ModelBuildingRequest,org.apache.maven.model.building.ModelProblemCollector):METHOD_NEW_DEFAULT</exclude>
             </excludes>
           </parameter>
         </configuration>
diff --git a/maven-model-builder/src/main/java/org/apache/maven/model/building/DefaultModelBuilder.java b/maven-model-builder/src/main/java/org/apache/maven/model/building/DefaultModelBuilder.java
index 70455795134..73d5f3b14a5 100644
--- a/maven-model-builder/src/main/java/org/apache/maven/model/building/DefaultModelBuilder.java
+++ b/maven-model-builder/src/main/java/org/apache/maven/model/building/DefaultModelBuilder.java
@@ -754,6 +754,7 @@ private void activateFileModel(
             profileInjector.injectProfile(inputModel, activeProfile, request, problems);
         }
 
+        modelValidator.validateExternalProfiles(activeExternalProfiles, inputModel, request, problems);
         for (Profile activeProfile : activeExternalProfiles) {
             profileInjector.injectProfile(inputModel, activeProfile, request, problems);
         }
diff --git a/maven-model-builder/src/main/java/org/apache/maven/model/validation/DefaultModelValidator.java b/maven-model-builder/src/main/java/org/apache/maven/model/validation/DefaultModelValidator.java
index 246e2f8b131..b51bbc22c73 100644
--- a/maven-model-builder/src/main/java/org/apache/maven/model/validation/DefaultModelValidator.java
+++ b/maven-model-builder/src/main/java/org/apache/maven/model/validation/DefaultModelValidator.java
@@ -24,6 +24,7 @@
 
 import java.io.File;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.Deque;
 import java.util.HashMap;
@@ -788,6 +789,54 @@ public void validateEffectiveModel(Model ma, ModelBuildingRequest request, Model
         }
     }
 
+    @Override
+    public void validateExternalProfiles(
+            List<org.apache.maven.model.Profile> activeExternalProfiles,
+            Model ma,
+            ModelBuildingRequest request,
+            ModelProblemCollector problems) {
+        org.apache.maven.api.model.Model m = ma.getDelegate();
+        // check for id clashes in repositories
+        for (Profile profile : activeExternalProfiles.stream()
+                .map(org.apache.maven.model.Profile::getDelegate)
+                .collect(Collectors.toList())) {
+            String externalRepositoriesSource = "external profile with id '" + profile.getId() + "' in settings.xml";
+            validateUniqueRepositoryIds(
+                    false, m.getRepositories(), profile.getRepositories(), externalRepositoriesSource, problems);
+            validateUniqueRepositoryIds(
+                    true,
+                    m.getPluginRepositories(),
+                    profile.getPluginRepositories(),
+                    externalRepositoriesSource,
+                    problems);
+        }
+    }
+
+    private void validateUniqueRepositoryIds(
+            boolean isPluginRepository,
+            Collection<Repository> pomRepositories,
+            Collection<Repository> externalRepositories,
+            String externalRepositoriesSource,
+            ModelProblemCollector problems) {
+        for (Repository externalRepository : externalRepositories) {
+            Optional<Repository> clashingPomRepository = pomRepositories.stream()
+                    .filter(r -> Objects.equals(r.getId(), externalRepository.getId()))
+                    .filter(r -> !Objects.equals(r.getUrl(), externalRepository.getUrl()))
+                    .findFirst();
+            if (clashingPomRepository.isPresent()) {
+                addViolation(
+                        problems,
+                        Severity.WARNING,
+                        Version.BASE,
+                        isPluginRepository ? "pluginRepositories.repository" : "repositories.repository",
+                        clashingPomRepository.get().getId(),
+                        "is overwritten by the repository with same id but having a different url from "
+                                + externalRepositoriesSource,
+                        clashingPomRepository.get());
+            }
+        }
+    }
+
     private void validate20RawDependencies(
             ModelProblemCollector problems,
             List<Dependency> dependencies,
diff --git a/maven-model-builder/src/main/java/org/apache/maven/model/validation/ModelValidator.java b/maven-model-builder/src/main/java/org/apache/maven/model/validation/ModelValidator.java
index 2817d95fc66..bb87370e0ef 100644
--- a/maven-model-builder/src/main/java/org/apache/maven/model/validation/ModelValidator.java
+++ b/maven-model-builder/src/main/java/org/apache/maven/model/validation/ModelValidator.java
@@ -18,7 +18,10 @@
  */
 package org.apache.maven.model.validation;
 
+import java.util.List;
+
 import org.apache.maven.model.Model;
+import org.apache.maven.model.Profile;
 import org.apache.maven.model.building.ModelBuildingRequest;
 import org.apache.maven.model.building.ModelProblemCollector;
 
@@ -49,6 +52,24 @@ default void validateFileModel(Model model, ModelBuildingRequest request, ModelP
      */
     void validateRawModel(Model model, ModelBuildingRequest request, ModelProblemCollector problems);
 
+    /**
+     * Checks the specified (raw) model for clashes with the passed active external profiles. The raw model is the
+     * file model + buildpom filter transformation and has not been subjected to inheritance, interpolation or profile/default injection.
+     *
+     * @param activeExternalProfiles the active profiles coming from external sources (settings.xml), must not be {@code null}
+     * @param model The model to validate, must not be {@code null}.
+     * @param request The model building request that holds further settings, must not be {@code null}.
+     * @param problems The container used to collect problems that were encountered, must not be {@code null}.
+     * @since 4.0.0
+     */
+    default void validateExternalProfiles(
+            List<Profile> activeExternalProfiles,
+            Model model,
+            ModelBuildingRequest request,
+            ModelProblemCollector problems) {
+        // do nothing
+    }
+
     /**
      * Checks the specified (effective) model for missing or invalid values. The effective model is fully assembled and
      * has undergone inheritance, interpolation and other model operations.