diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/KeysController.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/KeysController.java
index 61a16d1eb..3859c09d9 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/KeysController.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/KeysController.java
@@ -15,7 +15,9 @@ import io.swagger.v3.oas.annotations.media.Schema;
 import io.swagger.v3.oas.annotations.parameters.RequestBody;
 import io.swagger.v3.oas.annotations.responses.ApiResponse;
 import io.swagger.v3.oas.annotations.tags.Tag;
+import java.time.Duration;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -40,7 +42,6 @@ import org.whispersystems.textsecuregcm.auth.Anonymous;
 import org.whispersystems.textsecuregcm.auth.AuthenticatedAccount;
 import org.whispersystems.textsecuregcm.auth.DisabledPermittedAuthenticatedAccount;
 import org.whispersystems.textsecuregcm.auth.OptionalAccess;
-import org.whispersystems.textsecuregcm.entities.ECPreKey;
 import org.whispersystems.textsecuregcm.entities.ECSignedPreKey;
 import org.whispersystems.textsecuregcm.entities.KEMSignedPreKey;
 import org.whispersystems.textsecuregcm.entities.PreKeyCount;
@@ -59,6 +60,8 @@ import org.whispersystems.textsecuregcm.storage.AccountsManager;
 import org.whispersystems.textsecuregcm.storage.Device;
 import org.whispersystems.textsecuregcm.storage.KeysManager;
 import org.whispersystems.textsecuregcm.util.Util;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
 
 @SuppressWarnings("OptionalUsedAsFieldOrParameterType")
 @Path("/v2/keys")
@@ -237,43 +240,28 @@ public class KeysController {
             io.micrometer.core.instrument.Tag.of("wildcardDeviceId", String.valueOf("*".equals(deviceId)))))
         .increment();
 
-    final List<Device> devices = parseDeviceId(deviceId, target);
-    final List<PreKeyResponseItem> responseItems = new ArrayList<>(devices.size());
-
-    final List<CompletableFuture<Void>> tasks = devices.stream().map(device -> {
-          final CompletableFuture<Optional<ECPreKey>> unsignedEcPreKeyFuture =
-              keys.takeEC(targetIdentifier.uuid(), device.getId());
-
-          final CompletableFuture<Optional<ECSignedPreKey>> signedEcPreKeyFuture =
-              keys.getEcSignedPreKey(targetIdentifier.uuid(), device.getId());
-
-          final CompletableFuture<Optional<KEMSignedPreKey>> pqPreKeyFuture = returnPqKey
-              ? keys.takePQ(targetIdentifier.uuid(), device.getId())
-              : CompletableFuture.completedFuture(Optional.empty());
-
-          return CompletableFuture.allOf(unsignedEcPreKeyFuture, signedEcPreKeyFuture, pqPreKeyFuture)
-              .thenAccept(ignored -> {
-                final KEMSignedPreKey pqPreKey = pqPreKeyFuture.join().orElse(null);
-                final ECPreKey unsignedEcPreKey = unsignedEcPreKeyFuture.join().orElse(null);
-                final ECSignedPreKey signedEcPreKey = signedEcPreKeyFuture.join().orElse(null);
-
-                if (signedEcPreKey != null || unsignedEcPreKey != null || pqPreKey != null) {
-                  final int registrationId = switch (targetIdentifier.identityType()) {
-                    case ACI -> device.getRegistrationId();
-                    case PNI -> device.getPhoneNumberIdentityRegistrationId().orElse(device.getRegistrationId());
-                  };
-
-                  synchronized (responseItems) {
-                    responseItems.add(
-                        new PreKeyResponseItem(device.getId(), registrationId, signedEcPreKey, unsignedEcPreKey,
-                            pqPreKey));
-                  }
-                }
-              });
-        })
-        .toList();
-
-    CompletableFuture.allOf(tasks.toArray(new CompletableFuture[0])).join();
+    final List<PreKeyResponseItem> responseItems = Flux.fromIterable(parseDeviceId(deviceId, target))
+        .flatMap(device -> Mono.zip(
+            Mono.just(device),
+            Mono.fromFuture(() -> keys.getEcSignedPreKey(targetIdentifier.uuid(), device.getId())),
+            Mono.fromFuture(() -> keys.takeEC(targetIdentifier.uuid(), device.getId())),
+            Mono.fromFuture(() -> returnPqKey ? keys.takePQ(targetIdentifier.uuid(), device.getId())
+                : CompletableFuture.<Optional<KEMSignedPreKey>>completedFuture(Optional.empty()))
+        )).filter(keys -> keys.getT2().isPresent() || keys.getT3().isPresent() || keys.getT4().isPresent())
+        .map(deviceAndKeys -> {
+          final Device device = deviceAndKeys.getT1();
+          final int registrationId = switch (targetIdentifier.identityType()) {
+            case ACI -> device.getRegistrationId();
+            case PNI -> device.getPhoneNumberIdentityRegistrationId().orElse(device.getRegistrationId());
+          };
+          return new PreKeyResponseItem(device.getId(), registrationId,
+              deviceAndKeys.getT2().orElse(null),
+              deviceAndKeys.getT3().orElse(null),
+              deviceAndKeys.getT4().orElse(null));
+        }).collectList()
+        .timeout(Duration.ofSeconds(30))
+        .blockOptional()
+        .orElse(Collections.emptyList());
 
     final IdentityKey identityKey = target.getIdentityKey(targetIdentifier.identityType());