diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStore.java b/service/src/main/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStore.java
index 7d1f2a119..daa870b8c 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStore.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStore.java
@@ -7,17 +7,27 @@ package org.whispersystems.textsecuregcm.storage;
 
 import java.util.Map;
 import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
 import org.signal.libsignal.protocol.InvalidKeyException;
 import org.signal.libsignal.protocol.ecc.ECPublicKey;
 import org.whispersystems.textsecuregcm.entities.ECSignedPreKey;
 import org.whispersystems.textsecuregcm.util.AttributeValues;
+import org.whispersystems.textsecuregcm.util.ExceptionUtils;
 import software.amazon.awssdk.services.dynamodb.DynamoDbAsyncClient;
 import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
+import software.amazon.awssdk.services.dynamodb.model.ConditionalCheckFailedException;
+import software.amazon.awssdk.services.dynamodb.model.PutItemRequest;
 
 public class RepeatedUseECSignedPreKeyStore extends RepeatedUseSignedPreKeyStore<ECSignedPreKey> {
 
+  private final DynamoDbAsyncClient dynamoDbAsyncClient;
+  private final String tableName;
+
   public RepeatedUseECSignedPreKeyStore(final DynamoDbAsyncClient dynamoDbAsyncClient, final String tableName) {
     super(dynamoDbAsyncClient, tableName);
+
+    this.dynamoDbAsyncClient = dynamoDbAsyncClient;
+    this.tableName = tableName;
   }
 
   @Override
@@ -43,4 +53,21 @@ public class RepeatedUseECSignedPreKeyStore extends RepeatedUseSignedPreKeyStore
       throw new IllegalArgumentException(e);
     }
   }
+
+  public CompletableFuture<Boolean> storeIfAbsent(final UUID identifier, final long deviceId, final ECSignedPreKey signedPreKey) {
+    return dynamoDbAsyncClient.putItem(PutItemRequest.builder()
+            .tableName(tableName)
+            .item(getItemFromPreKey(identifier, deviceId, signedPreKey))
+            .conditionExpression("attribute_not_exists(#public_key)")
+            .expressionAttributeNames(Map.of("#public_key", ATTR_PUBLIC_KEY))
+            .build())
+        .thenApply(ignored -> true)
+        .exceptionally(throwable -> {
+          if (ExceptionUtils.unwrap(throwable) instanceof ConditionalCheckFailedException) {
+            return false;
+          }
+
+          throw ExceptionUtils.wrap(throwable);
+        });
+  }
 }
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStoreTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStoreTest.java
index 11c467ddc..1f6476d8c 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStoreTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/storage/RepeatedUseECSignedPreKeyStoreTest.java
@@ -6,11 +6,18 @@
 package org.whispersystems.textsecuregcm.storage;
 
 import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.RegisterExtension;
 import org.signal.libsignal.protocol.ecc.Curve;
 import org.signal.libsignal.protocol.ecc.ECKeyPair;
 import org.whispersystems.textsecuregcm.entities.ECSignedPreKey;
 import org.whispersystems.textsecuregcm.tests.util.KeysHelper;
+import java.util.Optional;
+import java.util.UUID;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 class RepeatedUseECSignedPreKeyStoreTest extends RepeatedUseSignedPreKeyStoreTest<ECSignedPreKey> {
 
@@ -39,4 +46,21 @@ class RepeatedUseECSignedPreKeyStoreTest extends RepeatedUseSignedPreKeyStoreTes
   protected ECSignedPreKey generateSignedPreKey() {
     return KeysHelper.signedECPreKey(currentKeyId++, IDENTITY_KEY_PAIR);
   }
+
+  @Test
+  void storeIfAbsent() {
+    final UUID identifier = UUID.randomUUID();
+    final long deviceIdWithExistingKey = 1;
+    final long deviceIdWithoutExistingKey = deviceIdWithExistingKey + 1;
+
+    final ECSignedPreKey originalSignedPreKey = generateSignedPreKey();
+
+    keyStore.store(identifier, deviceIdWithExistingKey, originalSignedPreKey).join();
+
+    assertFalse(keyStore.storeIfAbsent(identifier, deviceIdWithExistingKey, generateSignedPreKey()).join());
+    assertTrue(keyStore.storeIfAbsent(identifier, deviceIdWithoutExistingKey, generateSignedPreKey()).join());
+
+    assertEquals(Optional.of(originalSignedPreKey), keyStore.find(identifier, deviceIdWithExistingKey).join());
+    assertTrue(keyStore.find(identifier, deviceIdWithoutExistingKey).join().isPresent());
+  }
 }