diff --git a/SignalServiceKit/src/Messages/Attachments/TSAttachment.h b/SignalServiceKit/src/Messages/Attachments/TSAttachment.h
index be2a6849e5..978e3bae5f 100644
--- a/SignalServiceKit/src/Messages/Attachments/TSAttachment.h
+++ b/SignalServiceKit/src/Messages/Attachments/TSAttachment.h
@@ -29,7 +29,7 @@ typedef NS_ENUM(NSUInteger, TSAttachmentType) {
 @property (atomic) NSString *cdnKey;
 @property (atomic) UInt32 cdnNumber;
 @property (atomic, readwrite, nullable) NSData *encryptionKey;
-@property (nonatomic) NSString *contentType;
+@property (nonatomic, readonly) NSString *contentType;
 @property (nonatomic) TSAttachmentType attachmentType;
 
 // Though now required, may incorrectly be 0 on legacy attachments.
@@ -141,6 +141,10 @@ NS_DESIGNATED_INITIALIZER NS_SWIFT_NAME(init(grdbId:uniqueId:albumMessageId:atta
 
 + (NSString *)emojiForMimeType:(NSString *)contentType;
 
+// This should only ever be used before the attachment is saved,
+// after that point the content type will be already set.
+- (void)setDefaultContentType:(NSString *)contentType;
+
 #pragma mark - Update With...
 
 - (void)updateWithBlurHash:(NSString *)blurHash transaction:(SDSAnyWriteTransaction *)transaction;
diff --git a/SignalServiceKit/src/Messages/Attachments/TSAttachment.m b/SignalServiceKit/src/Messages/Attachments/TSAttachment.m
index 6a45301aa5..0575aae073 100644
--- a/SignalServiceKit/src/Messages/Attachments/TSAttachment.m
+++ b/SignalServiceKit/src/Messages/Attachments/TSAttachment.m
@@ -456,6 +456,13 @@ NSUInteger const TSAttachmentSchemaVersion = 5;
     [self.attachmentReadCache didRemoveAttachment:self transaction:transaction];
 }
 
+- (void)setDefaultContentType:(NSString *)contentType
+{
+    if ([self.contentType isEqualToString:OWSMimeTypeApplicationOctetStream]) {
+        _contentType = contentType;
+    }
+}
+
 #pragma mark - Update With...
 
 - (void)updateWithBlurHash:(NSString *)blurHash transaction:(SDSAnyWriteTransaction *)transaction
diff --git a/SignalServiceKit/src/Messages/Stickers/MessageSticker.swift b/SignalServiceKit/src/Messages/Stickers/MessageSticker.swift
index fd628fc124..d143576ec7 100644
--- a/SignalServiceKit/src/Messages/Stickers/MessageSticker.swift
+++ b/SignalServiceKit/src/Messages/Stickers/MessageSticker.swift
@@ -154,10 +154,7 @@ public class MessageSticker: MTLModel {
             throw StickerError.invalidInput
         }
 
-        if dataProto.contentType?.isEmpty != false && attachmentPointer.contentType == OWSMimeTypeApplicationOctetStream {
-            Logger.warn("Assuming sticker is webp, received with unspecified content-type")
-            attachmentPointer.contentType = OWSMimeTypeImageWebp
-        }
+        attachmentPointer.setDefaultContentType(OWSMimeTypeImageWebp)
 
         attachmentPointer.anyInsert(transaction: transaction)
         return attachmentPointer