diff --git a/core/src/main/java/google/registry/tmch/NordnUploadAction.java b/core/src/main/java/google/registry/tmch/NordnUploadAction.java
index df80682b2..b015b3ba9 100644
--- a/core/src/main/java/google/registry/tmch/NordnUploadAction.java
+++ b/core/src/main/java/google/registry/tmch/NordnUploadAction.java
@@ -39,8 +39,11 @@ import com.google.appengine.api.urlfetch.HTTPRequest;
 import com.google.appengine.api.urlfetch.HTTPResponse;
 import com.google.appengine.api.urlfetch.URLFetchService;
 import com.google.apphosting.api.DeadlineExceededException;
+import com.google.common.base.Joiner;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSortedSet;
+import com.google.common.collect.Ordering;
 import com.google.common.flogger.FluentLogger;
 import google.registry.config.RegistryConfig.Config;
 import google.registry.request.Action;
@@ -125,15 +128,19 @@ public final class NordnUploadAction implements Runnable {
    * delimited String.
    */
   static String convertTasksToCsv(List<TaskHandle> tasks, DateTime now, String columns) {
-    String header = String.format("1,%s,%d\n%s\n", now, tasks.size(), columns);
-    StringBuilder csv = new StringBuilder(header);
+    // Use a Set for deduping purposes so we can be idempotent in case tasks happened to be
+    // enqueued multiple times for a given domain create.
+    ImmutableSortedSet.Builder<String> builder =
+        new ImmutableSortedSet.Builder<>(Ordering.natural());
     for (TaskHandle task : checkNotNull(tasks)) {
       String payload = new String(task.getPayload(), UTF_8);
       if (!Strings.isNullOrEmpty(payload)) {
-        csv.append(payload).append("\n");
+        builder.add(payload + '\n');
       }
     }
-    return csv.toString();
+    ImmutableSortedSet<String> csvLines = builder.build();
+    String header = String.format("1,%s,%d\n%s\n", now, csvLines.size(), columns);
+    return header + Joiner.on("").join(csvLines);
   }
 
   /** Leases and returns all tasks from the queue with the specified tag tld, in batches. */
@@ -168,6 +175,11 @@ public final class NordnUploadAction implements Runnable {
                 : LordnTaskUtils.QUEUE_CLAIMS);
     String columns = phase.equals(PARAM_LORDN_PHASE_SUNRISE) ? COLUMNS_SUNRISE : COLUMNS_CLAIMS;
     List<TaskHandle> tasks = loadAllTasks(queue, tld);
+    // Note: This upload/task deletion isn't done atomically (it's not clear how one would do so
+    // anyway). As a result, it is possible that the upload might succeed yet the deletion of
+    // enqueued tasks might fail. If so, this would result in the same lines being uploaded to NORDN
+    // across mulitple uploads. This is probably OK; all that we really cannot have is a missing
+    // line.
     if (!tasks.isEmpty()) {
       String csvData = convertTasksToCsv(tasks, now, columns);
       uploadCsvToLordn(String.format("/LORDN/%s/%s", tld, phase), csvData);
diff --git a/core/src/test/java/google/registry/tmch/NordnUploadActionTest.java b/core/src/test/java/google/registry/tmch/NordnUploadActionTest.java
index dc74eb286..86e7be307 100644
--- a/core/src/test/java/google/registry/tmch/NordnUploadActionTest.java
+++ b/core/src/test/java/google/registry/tmch/NordnUploadActionTest.java
@@ -138,13 +138,26 @@ class NordnUploadActionTest {
   void test_convertTasksToCsv() {
     List<TaskHandle> tasks =
         ImmutableList.of(
-            makeTaskHandle("task1", "example", "csvLine1", "lordn-sunrise"),
             makeTaskHandle("task2", "example", "csvLine2", "lordn-sunrise"),
+            makeTaskHandle("task1", "example", "csvLine1", "lordn-sunrise"),
             makeTaskHandle("task3", "example", "ending", "lordn-sunrise"));
     assertThat(NordnUploadAction.convertTasksToCsv(tasks, clock.nowUtc(), "col1,col2"))
         .isEqualTo("1,2010-05-01T10:11:12.000Z,3\ncol1,col2\ncsvLine1\ncsvLine2\nending\n");
   }
 
+  @MockitoSettings(strictness = Strictness.LENIENT)
+  @Test
+  void test_convertTasksToCsv_dedupesDuplicates() {
+    List<TaskHandle> tasks =
+        ImmutableList.of(
+            makeTaskHandle("task2", "example", "csvLine2", "lordn-sunrise"),
+            makeTaskHandle("task1", "example", "csvLine1", "lordn-sunrise"),
+            makeTaskHandle("task3", "example", "ending", "lordn-sunrise"),
+            makeTaskHandle("task1", "example", "csvLine1", "lordn-sunrise"));
+    assertThat(NordnUploadAction.convertTasksToCsv(tasks, clock.nowUtc(), "col1,col2"))
+        .isEqualTo("1,2010-05-01T10:11:12.000Z,3\ncol1,col2\ncsvLine1\ncsvLine2\nending\n");
+  }
+
   @MockitoSettings(strictness = Strictness.LENIENT)
   @Test
   void test_convertTasksToCsv_doesntFailOnEmptyTasks() {