diff --git a/app/src/main/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModel.kt b/app/src/main/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModel.kt
index 201ac97b22..abba86236e 100644
--- a/app/src/main/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModel.kt
+++ b/app/src/main/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModel.kt
@@ -18,6 +18,7 @@ package org.groundplatform.android.ui.datacollection
 import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
+import java.util.concurrent.atomic.AtomicBoolean
 import javax.inject.Inject
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.CoroutineScope
@@ -112,6 +113,13 @@ internal constructor(
 
   private var draftsEnabled = true
 
+  /**
+   * Set while the final submission is being saved. The state stays [DataCollectionUiState.Ready]
+   * until the save completes, so without this, repeated taps on "Done" each save the same data
+   * again, creating duplicate LOIs and submissions.
+   */
+  private val isSubmitting = AtomicBoolean(false)
+
   init {
     viewModelScope.launch {
       val initResult =
@@ -296,22 +304,35 @@ internal constructor(
         if (!taskSequenceHandler.isLastPosition(task.id)) {
           moveToNextTask()
         } else {
-          clearDraft()
-          externalScope.launch(ioDispatcher) {
-            val submittedLoiId = saveChanges(uiState, getDeltas())
-            val loiReport =
-              getLoiReportUseCase.invoke(
-                loiName = getTypedLoiNameOrEmpty(),
-                loiId = submittedLoiId,
-                surveyId = uiState.surveyId,
-              )
-            _uiState.value = DataCollectionUiState.TaskSubmitted(loiReport)
-          }
+          submit(uiState)
         }
       }
     }
   }
 
+  /** Saves the collected data, ignoring the call if a save is already in progress. */
+  private fun submit(state: DataCollectionUiState.Ready) {
+    if (!isSubmitting.compareAndSet(false, true)) return
+    clearDraft()
+    externalScope.launch(ioDispatcher) {
+      val submittedLoiId =
+        try {
+          saveChanges(state, getDeltas())
+        } catch (e: Throwable) {
+          // Nothing was saved, so let the user try again.
+          isSubmitting.set(false)
+          throw e
+        }
+      val loiReport =
+        getLoiReportUseCase.invoke(
+          loiName = getTypedLoiNameOrEmpty(),
+          loiId = submittedLoiId,
+          surveyId = state.surveyId,
+        )
+      _uiState.value = DataCollectionUiState.TaskSubmitted(loiReport)
+    }
+  }
+
   fun onPreviousClicked(taskId: String) {
     val taskViewModel = getTaskViewModel(taskId) ?: return
     withReady { _ ->
diff --git a/app/src/test/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModelTest.kt b/app/src/test/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModelTest.kt
index ddaf073b3b..6a470df8af 100644
--- a/app/src/test/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModelTest.kt
+++ b/app/src/test/java/org/groundplatform/android/ui/datacollection/DataCollectionViewModelTest.kt
@@ -19,18 +19,27 @@ import androidx.lifecycle.SavedStateHandle
 import app.cash.turbine.test
 import com.google.common.truth.Truth.assertThat
 import dagger.hilt.android.testing.HiltAndroidTest
+import kotlinx.coroutines.CompletableDeferred
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.test.advanceUntilIdle
 import org.groundplatform.android.BaseHiltTest
 import org.groundplatform.android.FakeData
+import org.groundplatform.android.data.uuid.OfflineUuidGenerator
+import org.groundplatform.android.ui.common.ViewModelFactory
+import org.groundplatform.android.ui.datacollection.tasks.AbstractTaskViewModel
 import org.groundplatform.domain.model.task.Task
+import org.groundplatform.domain.usecases.submission.SubmitDataUseCase
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.mockito.kotlin.any
 import org.mockito.kotlin.anyOrNull
 import org.mockito.kotlin.doReturn
+import org.mockito.kotlin.doSuspendableAnswer
 import org.mockito.kotlin.mock
+import org.mockito.kotlin.times
+import org.mockito.kotlin.verify
 import org.mockito.kotlin.whenever
 import org.robolectric.RobolectricTestRunner
 
@@ -104,7 +113,53 @@ class DataCollectionViewModelTest : BaseHiltTest() {
     assertThat(viewModel.showExitWarning.value).isFalse()
   }
 
-  private suspend fun setupViewModel(result: DataCollectionUiState): DataCollectionViewModel {
+  @Test
+  fun `onNextClicked on last task submits only once while the save is in progress`() =
+    runWithTestDispatcher {
+      val saveBlocker = CompletableDeferred<String>()
+      val submitDataUseCase =
+        mock<SubmitDataUseCase>().apply {
+          whenever(invoke(anyOrNull(), any(), any(), any(), anyOrNull(), any()))
+            .doSuspendableAnswer { saveBlocker.await() }
+        }
+      val taskViewModel =
+        mock<AbstractTaskViewModel>().apply {
+          whenever(task) doReturn READY_STATE.tasks.first()
+          whenever(taskTaskData) doReturn MutableStateFlow(null)
+          whenever(validate()) doReturn null
+        }
+      val viewModelFactory =
+        mock<ViewModelFactory>().apply {
+          whenever(create(any<Class<AbstractTaskViewModel>>())) doReturn taskViewModel
+        }
+      val offlineUuidGenerator =
+        mock<OfflineUuidGenerator>().apply { whenever(generateUuid()) doReturn "collection-id" }
+      val viewModel =
+        setupViewModel(
+          READY_STATE,
+          submitDataUseCase = submitDataUseCase,
+          viewModelFactory = viewModelFactory,
+          offlineUuidGenerator = offlineUuidGenerator,
+        )
+      advanceUntilIdle()
+
+      repeat(3) { viewModel.onNextClicked("taskId") }
+      advanceUntilIdle()
+      saveBlocker.complete("loi-id")
+      advanceUntilIdle()
+
+      verify(submitDataUseCase, times(1))
+        .invoke(anyOrNull(), any(), any(), any(), anyOrNull(), any())
+      assertThat(viewModel.uiState.value)
+        .isInstanceOf(DataCollectionUiState.TaskSubmitted::class.java)
+    }
+
+  private suspend fun setupViewModel(
+    result: DataCollectionUiState,
+    submitDataUseCase: SubmitDataUseCase = mock(),
+    viewModelFactory: ViewModelFactory = mock(),
+    offlineUuidGenerator: OfflineUuidGenerator = mock(),
+  ): DataCollectionViewModel {
     val initializer =
       mock<DataCollectionInitializer>().apply {
         whenever(initialize(any(), any(), anyOrNull(), anyOrNull())) doReturn
@@ -116,9 +171,9 @@ class DataCollectionViewModelTest : BaseHiltTest() {
       externalScope = CoroutineScope(testDispatcher),
       ioDispatcher = testDispatcher,
       submissionRepository = mock(),
-      submitDataUseCase = mock(),
-      offlineUuidGenerator = mock(),
-      viewModelFactory = mock(),
+      submitDataUseCase = submitDataUseCase,
+      offlineUuidGenerator = offlineUuidGenerator,
+      viewModelFactory = viewModelFactory,
       dataCollectionInitializer = initializer,
       getLoiReportUseCase = mock(),
       loiReportExporter = mock(),