diff --git a/libheif/codecs/avif_boxes.cc b/libheif/codecs/avif_boxes.cc
index 584a5072b2..b03b7b950c 100644
--- a/libheif/codecs/avif_boxes.cc
+++ b/libheif/codecs/avif_boxes.cc
@@ -124,6 +124,7 @@ std::string Box_av1C::dump(Indent& indent) const
        << indent << "seq_level_idx_0: " << ((int) c.seq_level_idx_0) << "\n"
        << indent << "high_bitdepth: " << ((int) c.high_bitdepth) << "\n"
        << indent << "twelve_bit: " << ((int) c.twelve_bit) << "\n"
+       << indent << "monochrome: " << ((int) c.monochrome) << "\n"
        << indent << "chroma_subsampling_x: " << ((int) c.chroma_subsampling_x) << "\n"
        << indent << "chroma_subsampling_y: " << ((int) c.chroma_subsampling_y) << "\n"
        << indent << "chroma_sample_position: " << ((int) c.chroma_sample_position) << "\n"
diff --git a/libheif/codecs/avif_boxes.h b/libheif/codecs/avif_boxes.h
index d1e5c6e7a3..2ac2152900 100644
--- a/libheif/codecs/avif_boxes.h
+++ b/libheif/codecs/avif_boxes.h
@@ -68,7 +68,10 @@ friend class Box_mini;
     //unsigned int (8)[] configOBUs;
 
     heif_chroma get_heif_chroma() const {
-      if (chroma_subsampling_x==1 && chroma_subsampling_y==1) {
+      if (monochrome) {
+        return heif_chroma_monochrome;
+      }
+      else if (chroma_subsampling_x==1 && chroma_subsampling_y==1) {
         return heif_chroma_420;
       }
       else if (chroma_subsampling_x==1 && chroma_subsampling_y==0) {