diff --git a/scm-core/src/test/java/sonia/scm/util/ValidationUtilTest.java b/scm-core/src/test/java/sonia/scm/util/ValidationUtilTest.java
index 972ed95a2d..51ff906b8f 100644
--- a/scm-core/src/test/java/sonia/scm/util/ValidationUtilTest.java
+++ b/scm-core/src/test/java/sonia/scm/util/ValidationUtilTest.java
@@ -147,6 +147,10 @@ public class ValidationUtilTest
   public void testIsRepositoryNameValid() {
     String[] validPaths = {
       "scm",
+      "scm-",
+      "scm_",
+      "s_cm",
+      "s-cm",
       "s",
       "sc",
       ".hiddenrepo",
@@ -206,7 +210,8 @@ public class ValidationUtilTest
       "a/..b",
       "scm/main",
       "scm/plugins/git-plugin",
-      "scm/plugins/git-plugin"
+      "_scm",
+      "-scm"
     };
 
     for (String path : validPaths) {
diff --git a/scm-webapp/src/main/java/sonia/scm/update/MigrationWizardServlet.java b/scm-webapp/src/main/java/sonia/scm/update/MigrationWizardServlet.java
index 66c1006d4f..cd5f640c7b 100644
--- a/scm-webapp/src/main/java/sonia/scm/update/MigrationWizardServlet.java
+++ b/scm-webapp/src/main/java/sonia/scm/update/MigrationWizardServlet.java
@@ -10,6 +10,7 @@ import sonia.scm.event.ScmEventBus;
 import sonia.scm.update.repository.MigrationStrategy;
 import sonia.scm.update.repository.MigrationStrategyDao;
 import sonia.scm.update.repository.XmlRepositoryV1UpdateStep;
+import sonia.scm.util.ValidationUtil;
 
 import javax.inject.Inject;
 import javax.inject.Singleton;
@@ -18,13 +19,13 @@ import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import java.io.IOException;
 import java.io.PrintWriter;
-import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
-import java.util.Comparator;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
+
+import static java.util.Comparator.comparing;
 
 @Singleton
 class MigrationWizardServlet extends HttpServlet {
@@ -46,16 +47,20 @@ class MigrationWizardServlet extends HttpServlet {
 
   @Override
   protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
-    List<XmlRepositoryV1UpdateStep.V1Repository> repositoriesWithoutMigrationStrategies =
-      new ArrayList<>(repositoryV1UpdateStep.getRepositoriesWithoutMigrationStrategies());
-    repositoriesWithoutMigrationStrategies.sort(Comparator.comparing(XmlRepositoryV1UpdateStep.V1Repository::getPath));
+    List<RepositoryLineEntry> repositoryLineEntries = getRepositoryLineEntries();
+    doGet(req, resp, repositoryLineEntries);
+  }
 
+  protected void doGet(HttpServletRequest req, HttpServletResponse resp, List<RepositoryLineEntry> repositoryLineEntries) {
     HashMap<String, Object> model = new HashMap<>();
 
     model.put("contextPath", req.getContextPath());
     model.put("submitUrl", req.getRequestURI());
-    model.put("repositories", repositoriesWithoutMigrationStrategies);
+    model.put("repositories", repositoryLineEntries);
     model.put("strategies", getMigrationStrategies());
+    model.put("validationErrorsFound", repositoryLineEntries
+      .stream()
+      .anyMatch(entry -> entry.isNamespaceInvalid() || entry.isNameInvalid()));
 
     MustacheFactory mf = new DefaultMustacheFactory();
     Mustache template = mf.compile("templates/repository-migration.mustache");
@@ -64,16 +69,41 @@ class MigrationWizardServlet extends HttpServlet {
 
   @Override
   protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
-    resp.setStatus(200);
+    List<RepositoryLineEntry> repositoryLineEntries = getRepositoryLineEntries();
 
-    Arrays.stream(req.getParameterValues("ids")).forEach(
-      id -> {
-        String strategy = req.getParameter("strategy-" + id);
-        String namespace = req.getParameter("namespace-" + id);
-        String name = req.getParameter("name-" + id);
-        migrationStrategyDao.set(id, MigrationStrategy.valueOf(strategy), namespace, name);
+    boolean validationErrorFound = false;
+    for (RepositoryLineEntry repositoryLineEntry : repositoryLineEntries) {
+      String id = repositoryLineEntry.getId();
+      String namespace = req.getParameter("namespace-" + id);
+      String name = req.getParameter("name-" + id);
+      repositoryLineEntry.setNamespace(namespace);
+      repositoryLineEntry.setName(name);
+
+      if (!ValidationUtil.isRepositoryNameValid(namespace)) {
+        repositoryLineEntry.setNamespaceValid(false);
+        validationErrorFound = true;
       }
-    );
+      if (!ValidationUtil.isRepositoryNameValid(name)) {
+        repositoryLineEntry.setNameValid(false);
+        validationErrorFound = true;
+      }
+    }
+
+    if (validationErrorFound) {
+      doGet(req, resp, repositoryLineEntries);
+      return;
+    }
+
+    repositoryLineEntries.stream()
+      .map(RepositoryLineEntry::getId)
+      .forEach(
+        id -> {
+          String strategy = req.getParameter("strategy-" + id);
+          String namespace = req.getParameter("namespace-" + id);
+          String name = req.getParameter("name-" + id);
+          migrationStrategyDao.set(id, MigrationStrategy.valueOf(strategy), namespace, name);
+        }
+      );
 
     MustacheFactory mf = new DefaultMustacheFactory();
     Mustache template = mf.compile("templates/repository-migration-restart.mustache");
@@ -81,9 +111,20 @@ class MigrationWizardServlet extends HttpServlet {
 
     respondWithTemplate(resp, model, template);
 
+    resp.setStatus(200);
+
     ScmEventBus.getInstance().post(new RestartEvent(MigrationWizardServlet.class, "wrote migration data"));
   }
 
+  private List<RepositoryLineEntry> getRepositoryLineEntries() {
+    List<XmlRepositoryV1UpdateStep.V1Repository> repositoriesWithoutMigrationStrategies =
+      repositoryV1UpdateStep.getRepositoriesWithoutMigrationStrategies();
+    return repositoriesWithoutMigrationStrategies.stream()
+      .map(RepositoryLineEntry::new)
+      .sorted(comparing(RepositoryLineEntry::getPath))
+      .collect(Collectors.toList());
+  }
+
   private MigrationStrategy[] getMigrationStrategies() {
     return MigrationStrategy.values();
   }
@@ -101,4 +142,66 @@ class MigrationWizardServlet extends HttpServlet {
     writer.flush();
     resp.setStatus(200);
   }
+
+  private static class RepositoryLineEntry {
+    private final String id;
+    private final String type;
+    private final String path;
+    private String namespace;
+    private String name;
+    private boolean namespaceValid = true;
+    private boolean nameValid = true;
+
+    public RepositoryLineEntry(XmlRepositoryV1UpdateStep.V1Repository repository) {
+      this.id = repository.getId();
+      this.type = repository.getType();
+      this.path = repository.getPath();
+      this.namespace = repository.getNewNamespace();
+      this.name = repository.getNewName();
+    }
+
+    public String getId() {
+      return id;
+    }
+
+    public String getType() {
+      return type;
+    }
+
+    public String getPath() {
+      return path;
+    }
+
+    public String getNamespace() {
+      return namespace;
+    }
+
+    public String getName() {
+      return name;
+    }
+
+    public void setNamespace(String namespace) {
+      this.namespace = namespace;
+    }
+
+    public void setName(String name) {
+      this.name = name;
+    }
+
+    public void setNamespaceValid(boolean namespaceValid) {
+      this.namespaceValid = namespaceValid;
+    }
+
+    public void setNameValid(boolean nameValid) {
+      this.nameValid = nameValid;
+    }
+
+    public boolean isNamespaceInvalid() {
+      return !namespaceValid;
+    }
+
+    public boolean isNameInvalid() {
+      return !nameValid;
+    }
+  }
 }
diff --git a/scm-webapp/src/main/resources/templates/repository-migration.mustache b/scm-webapp/src/main/resources/templates/repository-migration.mustache
index 5a9085fb4b..9d7e5e0a0b 100644
--- a/scm-webapp/src/main/resources/templates/repository-migration.mustache
+++ b/scm-webapp/src/main/resources/templates/repository-migration.mustache
@@ -41,14 +41,24 @@
               </p>
             </div>
             <hr>
+          {{#validationErrorsFound}}
+            <div class="notification is-danger">Please correct the invalid namespaces or names below and try again.</div>
+            <hr>
+          {{/validationErrorsFound}}
             <form action="{{submitUrl}}" method="post">
               <table class="card-table table is-hoverable is-fullwidth">
                 <tr>
                   <th>Original name</th>
                   <th>Type</th>
-                  <th>New namespace</th>
-                  <th>New name</th>
-                  <th>Strategy</th>
+                  <th>New namespace
+                    <span class="tooltip is-tooltip-right is-tooltip-multiline t-tooltip-0-1-38" data-tooltip="The namespace of the repository. This will be part op the url. The new namespace must consist of letters, digits, dots, dashes and underscores (it must not start with a dash or a underscore)."><i class="fa fa-question-circle has-text-info t-textinfo-0-1-10"></i></span>
+                  </th>
+                  <th>New name
+                    <span class="tooltip is-tooltip-right is-tooltip-multiline t-tooltip-0-1-38" data-tooltip="The name of the repository. This will be part op the url. The new name must consist of letters, digits, dots, dashes and underscores (it must not start with a dash or a underscore)."><i class="fa fa-question-circle has-text-info t-textinfo-0-1-10"></i></span>
+                  </th>
+                  <th>Strategy
+                    <span class="tooltip is-tooltip-right is-tooltip-multiline t-tooltip-0-1-38" data-tooltip="The strategy used to migrate the data directory of the repository. See above for the means of the different strategies."><i class="fa fa-question-circle has-text-info t-textinfo-0-1-10"></i></span>
+                  </th>
                 </tr>
                 {{#repositories}}
                   <tr>
@@ -59,10 +69,10 @@
                       {{type}}
                     </td>
                     <td>
-                      <input class="input" type="text" name="namespace-{{id}}" value="{{newNamespace}}">
+                      <input class="input {{#namespaceInvalid}}is-danger{{/namespaceInvalid}}" type="text" name="namespace-{{id}}" value="{{namespace}}">
                     </td>
                     <td>
-                      <input class="input" type="text" name="name-{{id}}" value="{{newName}}">
+                      <input class="input {{#nameInvalid}}is-danger{{/nameInvalid}}" type="text" name="name-{{id}}" value="{{name}}">
                     </td>
                     <td>
                       <div class="field">
@@ -78,9 +88,6 @@
                   </tr>
                 {{/repositories}}
               </table>
-              {{#repositories}}
-                <input type="hidden" name="ids" value="{{id}}">
-              {{/repositories}}
               <button class="button is-primary" type="submit">Submit</button>
             </form>
           </div>