diff --git a/src/main/kotlin/org/wfanet/measurement/kingdom/deploy/gcloud/spanner/writers/ConfirmComputationParticipant.kt b/src/main/kotlin/org/wfanet/measurement/kingdom/deploy/gcloud/spanner/writers/ConfirmComputationParticipant.kt
index 34f627c7b03..a050ba9609b 100644
--- a/src/main/kotlin/org/wfanet/measurement/kingdom/deploy/gcloud/spanner/writers/ConfirmComputationParticipant.kt
+++ b/src/main/kotlin/org/wfanet/measurement/kingdom/deploy/gcloud/spanner/writers/ConfirmComputationParticipant.kt
@@ -14,11 +14,16 @@
 
 package org.wfanet.measurement.kingdom.deploy.gcloud.spanner.writers
 
+import com.google.cloud.spanner.Statement
 import com.google.cloud.spanner.Value
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.toList
 import org.wfanet.measurement.common.identity.ExternalId
 import org.wfanet.measurement.common.identity.InternalId
+import org.wfanet.measurement.gcloud.spanner.bind
 import org.wfanet.measurement.gcloud.spanner.bufferUpdateMutation
 import org.wfanet.measurement.gcloud.spanner.set
+import org.wfanet.measurement.gcloud.spanner.statement
 import org.wfanet.measurement.internal.kingdom.ComputationParticipant
 import org.wfanet.measurement.internal.kingdom.ConfirmComputationParticipantRequest
 import org.wfanet.measurement.internal.kingdom.Measurement
@@ -106,13 +111,17 @@ class ConfirmComputationParticipant(private val request: ConfirmComputationParti
       set("State" to NEXT_COMPUTATION_PARTICIPANT_STATE)
     }
 
-    val otherDuchyIds: List<InternalId> =
-      DuchyIds.entries.map { InternalId(it.internalDuchyId) }.filter { it.value != duchyId }
+    val duchyIds: List<InternalId> =
+      getComputationParticipantsDuchyIds(
+          InternalId(measurementConsumerId),
+          InternalId(measurementId)
+        )
+        .filter { it.value != duchyId }
 
     if (
       computationParticipantsInState(
         transactionContext,
-        otherDuchyIds,
+        duchyIds,
         InternalId(measurementConsumerId),
         InternalId(measurementId),
         NEXT_COMPUTATION_PARTICIPANT_STATE
@@ -136,6 +145,29 @@ class ConfirmComputationParticipant(private val request: ConfirmComputationParti
     return computationParticipant.copy { state = NEXT_COMPUTATION_PARTICIPANT_STATE }
   }
 
+  private suspend fun TransactionScope.getComputationParticipantsDuchyIds(
+    measurementConsumerId: InternalId,
+    measurementId: InternalId
+  ): List<InternalId> {
+    val sql =
+      """
+      SELECT DuchyId
+      FROM ComputationParticipants
+      WHERE MeasurementConsumerId = @measurement_consumer_id
+        AND MeasurementId = @measurement_id
+      """
+        .trimIndent()
+    val statement: Statement =
+      statement(sql) {
+        bind("measurement_consumer_id" to measurementConsumerId.value)
+        bind("measurement_id" to measurementId)
+      }
+    return transactionContext
+      .executeQuery(statement)
+      .map { InternalId(it.getLong("DuchyId")) }
+      .toList()
+  }
+
   override fun ResultScope<ComputationParticipant>.buildResult(): ComputationParticipant {
     return checkNotNull(transactionResult).copy { updateTime = commitTimestamp.toProto() }
   }
diff --git a/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/ComputationParticipantsServiceTest.kt b/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/ComputationParticipantsServiceTest.kt
index 2d06fa6aca0..35149b89917 100644
--- a/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/ComputationParticipantsServiceTest.kt
+++ b/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/ComputationParticipantsServiceTest.kt
@@ -129,8 +129,9 @@ abstract class ComputationParticipantsServiceTest<T : ComputationParticipantsCor
     accountsService = services.accountsService
   }
 
-  private fun createDuchyCertificates() {
-    val externalDuchyIds = DUCHIES.map { it.externalDuchyId }
+  private fun createDuchyCertificates(
+    externalDuchyIds: List<String> = DUCHIES.map { it.externalDuchyId }
+  ) {
     duchyCertificates =
       externalDuchyIds.associateWith { externalDuchyId ->
         runBlocking { population.createDuchyCertificate(certificatesService, externalDuchyId) }
@@ -699,6 +700,87 @@ abstract class ComputationParticipantsServiceTest<T : ComputationParticipantsCor
     assertThat(updatedMeasurement.state).isEqualTo(Measurement.State.PENDING_COMPUTATION)
   }
 
+  @Test
+  fun `confirmComputationParticipant succeeds with a subset of registered duchies`() = runBlocking {
+    val duchies = DUCHIES.dropLast(1)
+    createDuchyCertificates(duchies.map { it.externalDuchyId })
+    val measurement =
+      population.createComputedMeasurement(
+        measurementsService,
+        population.createMeasurementConsumer(measurementConsumersService, accountsService),
+        "measurement",
+        population.createDataProvider(
+          dataProvidersService,
+          listOf(Population.AGGREGATOR_DUCHY.externalDuchyId)
+        ),
+      )
+
+    val setParticipantRequisitionParamsDetails = liquidLegionsV2Details {
+      elGamalPublicKey = EL_GAMAL_PUBLIC_KEY
+      elGamalPublicKeySignature = EL_GAMAL_PUBLIC_KEY_SIGNATURE
+    }
+
+    // Step 1 - SetParticipantRequisitionParams for all ComputationParticipants. This transitions
+    // the measurement state to PENDING_REQUISITION_FULFILLMENT.
+    for (duchyCertificate in duchyCertificates.values) {
+      computationParticipantsService.setParticipantRequisitionParams(
+        setParticipantRequisitionParamsRequest {
+          externalComputationId = measurement.externalComputationId
+          externalDuchyId = duchyCertificate.externalDuchyId
+          externalDuchyCertificateId = duchyCertificate.externalCertificateId
+          liquidLegionsV2 = setParticipantRequisitionParamsDetails
+        }
+      )
+    }
+
+    val requisitions =
+      requisitionsService
+        .streamRequisitions(
+          streamRequisitionsRequest {
+            filter = filter {
+              externalMeasurementConsumerId = measurement.externalMeasurementConsumerId
+              externalMeasurementId = measurement.externalMeasurementId
+            }
+          }
+        )
+        .toList()
+
+    // Step 2 - FulfillRequisitions for all Requisitions. This transitions the measurement state to
+    // PENDING_PARTICIPANT_CONFIRMATION.
+    val nonce = 3127743798281582205L
+    for ((requisition, duchy) in requisitions zip duchies) {
+      requisitionsService.fulfillRequisition(
+        fulfillRequisitionRequest {
+          externalRequisitionId = requisition.externalRequisitionId
+          this.nonce = nonce
+          computedParams = computedRequisitionParams {
+            externalComputationId = measurement.externalComputationId
+            externalFulfillingDuchyId = duchy.externalDuchyId
+          }
+        }
+      )
+    }
+
+    // Step 3 - ConfirmComputationParticipant for all ComputationParticipants. This transitions
+    // the measurement state to PENDING_COMPUTATION.
+    for (duchy in duchies) {
+      computationParticipantsService.confirmComputationParticipant(
+        confirmComputationParticipantRequest {
+          externalComputationId = measurement.externalComputationId
+          this.externalDuchyId = duchy.externalDuchyId
+        }
+      )
+    }
+
+    val updatedMeasurement =
+      measurementsService.getMeasurementByComputationId(
+        getMeasurementByComputationIdRequest {
+          this.externalComputationId = measurement.externalComputationId
+        }
+      )
+    assertThat(updatedMeasurement.state).isEqualTo(Measurement.State.PENDING_COMPUTATION)
+  }
+
   @Test
   fun `failComputationParticipant fails due to illegal  measurement state`() = runBlocking {
     createDuchyCertificates()
diff --git a/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/Population.kt b/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/Population.kt
index 090f34f6388..c64459aaff2 100644
--- a/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/Population.kt
+++ b/src/main/kotlin/org/wfanet/measurement/kingdom/service/internal/testing/Population.kt
@@ -145,6 +145,8 @@ class Population(val clock: Clock, val idGenerator: IdGenerator) {
 
   suspend fun createDataProvider(
     dataProvidersService: DataProvidersCoroutineImplBase,
+    requiredDuchiesList: List<String> =
+      listOf(WORKER1_DUCHY.externalDuchyId, WORKER2_DUCHY.externalDuchyId),
     notValidBefore: Instant = clock.instant(),
     notValidAfter: Instant = notValidBefore.plus(365L, ChronoUnit.DAYS),
     customize: (DataProviderKt.Dsl.() -> Unit)? = null
@@ -165,8 +167,7 @@ class Population(val clock: Clock, val idGenerator: IdGenerator) {
             publicKeySignature = "EDP public key signature".toByteStringUtf8()
             publicKeySignatureAlgorithmOid = "2.9999"
           }
-        requiredExternalDuchyIds += WORKER1_DUCHY.externalDuchyId
-        requiredExternalDuchyIds += WORKER2_DUCHY.externalDuchyId
+        requiredExternalDuchyIds += requiredDuchiesList
         customize?.invoke(this)
       }
     )