diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
index 23ed1a5bb..fa3eb7aec 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java
@@ -114,6 +114,7 @@ import org.whispersystems.textsecuregcm.limits.RateLimitResetMetricsManager;
 import org.whispersystems.textsecuregcm.limits.RateLimiters;
 import org.whispersystems.textsecuregcm.limits.UnsealedSenderRateLimiter;
 import org.whispersystems.textsecuregcm.liquibase.NameableMigrationsBundle;
+import org.whispersystems.textsecuregcm.mappers.CompletionExceptionMapper;
 import org.whispersystems.textsecuregcm.mappers.DeviceLimitExceededExceptionMapper;
 import org.whispersystems.textsecuregcm.mappers.IOExceptionMapper;
 import org.whispersystems.textsecuregcm.mappers.ImpossiblePhoneNumberExceptionMapper;
@@ -743,6 +744,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
 
     List.of(
         new LoggingUnhandledExceptionMapper(),
+        new CompletionExceptionMapper(),
         new IOExceptionMapper(),
         new RateLimitExceededExceptionMapper(),
         new InvalidWebsocketAddressExceptionMapper(),
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/mappers/CompletionExceptionMapper.java b/service/src/main/java/org/whispersystems/textsecuregcm/mappers/CompletionExceptionMapper.java
new file mode 100644
index 000000000..829fcc7c9
--- /dev/null
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/mappers/CompletionExceptionMapper.java
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2020 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.mappers;
+
+import java.util.concurrent.CompletionException;
+import javax.ws.rs.core.Context;
+import javax.ws.rs.core.Response;
+import javax.ws.rs.ext.ExceptionMapper;
+import javax.ws.rs.ext.Provider;
+import javax.ws.rs.ext.Providers;
+
+@Provider
+public class CompletionExceptionMapper implements ExceptionMapper<CompletionException> {
+
+  @Context
+  private Providers providers;
+
+  @Override
+  public Response toResponse(final CompletionException exception) {
+    final Throwable cause = exception.getCause();
+
+    if (cause != null) {
+      final Class type = cause.getClass();
+      return providers.getExceptionMapper(type).toResponse(cause);
+    }
+
+    return Response.serverError().build();
+  }
+}