diff --git a/core/src/main/java/google/registry/ui/server/registrar/RegistryLockPostAction.java b/core/src/main/java/google/registry/ui/server/registrar/RegistryLockPostAction.java
index a21e0e5d8..2d230d815 100644
--- a/core/src/main/java/google/registry/ui/server/registrar/RegistryLockPostAction.java
+++ b/core/src/main/java/google/registry/ui/server/registrar/RegistryLockPostAction.java
@@ -30,6 +30,7 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.flogger.FluentLogger;
 import com.google.gson.Gson;
 import google.registry.config.RegistryConfig.Config;
+import google.registry.flows.domain.DomainFlowUtils;
 import google.registry.model.registrar.Registrar;
 import google.registry.model.registrar.RegistrarContact;
 import google.registry.request.Action;
@@ -118,6 +119,7 @@ public class RegistryLockPostAction implements Runnable, JsonActionRunner.JsonAc
       String registrarId = postInput.registrarId;
       checkArgument(!Strings.isNullOrEmpty(registrarId), "Missing key for registrarId");
       checkArgument(!Strings.isNullOrEmpty(postInput.domainName), "Missing key for domainName");
+      DomainFlowUtils.validateDomainName(postInput.domainName);
       checkNotNull(postInput.isLock, "Missing key for isLock");
       UserAuthInfo userAuthInfo =
           authResult
diff --git a/core/src/test/java/google/registry/ui/server/registrar/RegistryLockPostActionTest.java b/core/src/test/java/google/registry/ui/server/registrar/RegistryLockPostActionTest.java
index ee6b416c1..f2937b1d3 100644
--- a/core/src/test/java/google/registry/ui/server/registrar/RegistryLockPostActionTest.java
+++ b/core/src/test/java/google/registry/ui/server/registrar/RegistryLockPostActionTest.java
@@ -280,6 +280,16 @@ public final class RegistryLockPostActionTest {
     assertFailureWithMessage(response, "Missing key for domainName");
   }
 
+  @Test
+  public void testFailure_nonPunycodeDomainName() {
+    Map<String, ?> response = action.handleJsonRequest(ImmutableMap.of(
+        "isLock", true,
+        "registrarId", "TheRegistrar",
+        "domainName", "example.みんな",
+        "password", "hi"));
+    assertFailureWithMessage(response, "Domain names can only contain a-z, 0-9, '.' and '-'");
+  }
+
   @Test
   public void testFailure_noLockParam() {
     Map<String, ?> response =