diff --git a/SignalServiceKit/src/Messages/OWSMessageManager.m b/SignalServiceKit/src/Messages/OWSMessageManager.m
index 68a20d28c..033c1976f 100644
--- a/SignalServiceKit/src/Messages/OWSMessageManager.m
+++ b/SignalServiceKit/src/Messages/OWSMessageManager.m
@@ -528,12 +528,18 @@ NS_ASSUME_NONNULL_BEGIN
     }
 
     // Send delivery receipts for "valid data" messages received via UD.
-    BOOL wasReceivedByUD = envelope.type == SSKProtoEnvelopeTypeUnidentifiedSender;
+    BOOL wasReceivedByUD = [self wasReceivedByUD:envelope];
     if (wasReceivedByUD) {
         [self.outgoingReceiptManager enqueueDeliveryReceiptForEnvelope:envelope];
     }
 }
 
+- (BOOL)wasReceivedByUD:(SSKProtoEnvelope *)envelope
+{
+    return (
+        envelope.type == SSKProtoEnvelopeTypeUnidentifiedSender && (!envelope.hasSource || envelope.source.length < 1));
+}
+
 - (void)sendGroupInfoRequest:(NSData *)groupId
                     envelope:(SSKProtoEnvelope *)envelope
                  transaction:(YapDatabaseReadWriteTransaction *)transaction
@@ -1121,7 +1127,7 @@ NS_ASSUME_NONNULL_BEGIN
     NSData *groupId = dataMessage.group ? dataMessage.group.id : nil;
     OWSContact *_Nullable contact = [OWSContacts contactForDataMessage:dataMessage transaction:transaction];
     NSNumber *_Nullable serverTimestamp = (envelope.hasServerTimestamp ? @(envelope.serverTimestamp) : nil);
-    BOOL wasReceivedByUD = envelope.type == SSKProtoEnvelopeTypeUnidentifiedSender;
+    BOOL wasReceivedByUD = [self wasReceivedByUD:envelope];
 
     if (dataMessage.group.type == SSKProtoGroupContextTypeRequestInfo) {
         [self handleGroupInfoRequest:envelope dataMessage:dataMessage transaction:transaction];
diff --git a/SignalServiceKit/src/Messages/OWSMessageSender.m b/SignalServiceKit/src/Messages/OWSMessageSender.m
index 7c5b6655b..53c359a67 100644
--- a/SignalServiceKit/src/Messages/OWSMessageSender.m
+++ b/SignalServiceKit/src/Messages/OWSMessageSender.m
@@ -1053,6 +1053,25 @@ NSString *const OWSMessageSenderRateLimitedException = @"RateLimitedException";
         }
     }
 
+    for (NSDictionary *deviceMessage in deviceMessages) {
+        NSNumber *_Nullable messageType = deviceMessage[@"type"];
+        OWSAssertDebug(messageType);
+        BOOL hasValidMessageType;
+        if (messageSend.isUDSend) {
+            hasValidMessageType = [messageType isEqualToNumber:@(TSUnidentifiedSenderMessageType)];
+        } else {
+            hasValidMessageType = ([messageType isEqualToNumber:@(TSEncryptedWhisperMessageType)] ||
+                [messageType isEqualToNumber:@(TSPreKeyWhisperMessageType)]);
+        }
+
+        if (!hasValidMessageType) {
+            OWSFailDebug(@"Invalid message type: %@", messageType);
+            NSError *error = OWSErrorMakeFailedToSendOutgoingMessageError();
+            [error setIsRetryable:NO];
+            return messageSend.failure(error);
+        }
+    }
+
     if (deviceMessages.count == 0) {
         // This might happen:
         //