diff --git a/src/write.c b/src/write.c
index cf4e1c7932..528292080b 100644
--- a/src/write.c
+++ b/src/write.c
@@ -3134,6 +3134,7 @@ avifResult avifEncoderFinish(avifEncoder * encoder, avifRWData * output)
     // -----------------------------------------------------------------------
     // Harvest configuration properties from sequence headers
 
+    avifBool isMA1B = AVIF_TRUE;
     for (uint32_t itemIndex = 0; itemIndex < encoder->data->items.count; ++itemIndex) {
         avifEncoderItem * item = &encoder->data->items.item[itemIndex];
         if (item->encodeOutput->samples.count > 0) {
@@ -3142,6 +3143,11 @@ avifResult avifEncoderFinish(avifEncoder * encoder, avifRWData * output)
             AVIF_CHECKERR(avifSequenceHeaderParse(&sequenceHeader, (const avifROData *)&firstSample->data, codecType),
                           avifGetErrorForItemCategory(item->itemCategory));
             item->av1C = sequenceHeader.av1C;
+            //  The MA1B brand: The AV1 profile shall be the Main Profile and
+            //  the level shall be 5.1 or lower.
+            if (item->av1C.seqProfile != 0 || item->av1C.seqLevelIdx0 > 13) {
+                isMA1B = AVIF_FALSE;
+            }
         }
     }
 
@@ -3239,10 +3245,11 @@ avifResult avifEncoderFinish(avifEncoder * encoder, avifRWData * output)
     }                                                                      //
     AVIF_CHECKRES(avifRWStreamWriteChars(&s, "mif1", 4));                  // ... compatible_brands[]
     AVIF_CHECKRES(avifRWStreamWriteChars(&s, "miaf", 4));                  // ... compatible_brands[]
+    if (isMA1B) {                                                          //
+        AVIF_CHECKRES(avifRWStreamWriteChars(&s, "MA1B", 4));              // ... compatible_brands[]
+    }                                                                      //
     if ((imageMetadata->depth == 8) || (imageMetadata->depth == 10)) {     //
-        if (imageMetadata->yuvFormat == AVIF_PIXEL_FORMAT_YUV420) {        //
-            AVIF_CHECKRES(avifRWStreamWriteChars(&s, "MA1B", 4));          // ... compatible_brands[]
-        } else if (imageMetadata->yuvFormat == AVIF_PIXEL_FORMAT_YUV444) { //
+        if (imageMetadata->yuvFormat == AVIF_PIXEL_FORMAT_YUV444) {        //
             AVIF_CHECKRES(avifRWStreamWriteChars(&s, "MA1A", 4));          // ... compatible_brands[]
         }
     }