diff --git a/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceMessageSender.java b/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceMessageSender.java
index 2a1711e052..dc4fb6cba0 100644
--- a/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceMessageSender.java
+++ b/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceMessageSender.java
@@ -22,11 +22,10 @@ import org.whispersystems.signalservice.api.crypto.SignalServiceCipher;
 import org.whispersystems.signalservice.api.crypto.UnidentifiedAccess;
 import org.whispersystems.signalservice.api.crypto.UnidentifiedAccessPair;
 import org.whispersystems.signalservice.api.crypto.UntrustedIdentityException;
-import org.whispersystems.signalservice.api.groupsv2.ClientZkOperations;
 import org.whispersystems.signalservice.api.messages.SendMessageResult;
 import org.whispersystems.signalservice.api.messages.SignalServiceAttachment;
-import org.whispersystems.signalservice.api.messages.SignalServiceAttachmentRemoteId;
 import org.whispersystems.signalservice.api.messages.SignalServiceAttachmentPointer;
+import org.whispersystems.signalservice.api.messages.SignalServiceAttachmentRemoteId;
 import org.whispersystems.signalservice.api.messages.SignalServiceAttachmentStream;
 import org.whispersystems.signalservice.api.messages.SignalServiceDataMessage;
 import org.whispersystems.signalservice.api.messages.SignalServiceGroup;
@@ -503,6 +502,13 @@ public class SignalServiceMessageSender {
 
     if (!pointers.isEmpty()) {
       builder.addAllAttachments(pointers);
+
+      for (AttachmentPointer pointer : pointers) {
+        if (pointer.getAttachmentIdentifierCase() == AttachmentPointer.AttachmentIdentifierCase.CDNKEY || pointer.getCdnNumber() != 0) {
+          builder.setRequiredProtocolVersion(Math.max(DataMessage.ProtocolVersion.CDN_SELECTOR_ATTACHMENTS_VALUE, builder.getRequiredProtocolVersion()));
+          break;
+        }
+      }
     }
 
     if (message.getBody().isPresent()) {
diff --git a/libsignal/service/src/main/proto/SignalService.proto b/libsignal/service/src/main/proto/SignalService.proto
index 702535557d..e1afb82c60 100644
--- a/libsignal/service/src/main/proto/SignalService.proto
+++ b/libsignal/service/src/main/proto/SignalService.proto
@@ -187,12 +187,13 @@ message DataMessage {
   enum ProtocolVersion {
     option allow_alias = true;
 
-    INITIAL         = 0;
-    MESSAGE_TIMERS  = 1;
-    VIEW_ONCE       = 2;
-    VIEW_ONCE_VIDEO = 3;
-    REACTIONS       = 4;
-    CURRENT         = 4;
+    INITIAL                  = 0;
+    MESSAGE_TIMERS           = 1;
+    VIEW_ONCE                = 2;
+    VIEW_ONCE_VIDEO          = 3;
+    REACTIONS                = 4;
+    CDN_SELECTOR_ATTACHMENTS = 5;
+    CURRENT                  = 5;
   }
 
   optional string             body                    = 1;