diff --git a/apps/avifgainmaputil/swapbase_command.cc b/apps/avifgainmaputil/swapbase_command.cc
index 752f892ff7..5333b02428 100644
--- a/apps/avifgainmaputil/swapbase_command.cc
+++ b/apps/avifgainmaputil/swapbase_command.cc
@@ -54,9 +54,13 @@ avifResult SwapBaseCommand::Run() {
                 : std::max(decoder->image->depth,
                            decoder->image->gainMap.image->depth);
   }
-  ImagePtr new_base(
-      avifImageCreate(decoder->image->width, decoder->image->height, depth,
-                      (avifPixelFormat)arg_image_read_.pixel_format.value()));
+  avifPixelFormat pixel_format =
+      (avifPixelFormat)arg_image_read_.pixel_format.value();
+  if (pixel_format == AVIF_PIXEL_FORMAT_NONE) {
+    pixel_format = AVIF_PIXEL_FORMAT_YUV444;
+  }
+  ImagePtr new_base(avifImageCreate(
+      decoder->image->width, decoder->image->height, depth, pixel_format));
   // The gain map's cicp values are those of the 'tmap' item and describe the
   // image obtained by fully applying the gain map. See ISO/IEC JTC 1/SC 29/WG 3
   // m64379v1 4.1.1: A tmap derived item shall be associated with a colr item
diff --git a/apps/avifgainmaputil/tonemap_command.cc b/apps/avifgainmaputil/tonemap_command.cc
index 19b3c2fc03..496a9d1c53 100644
--- a/apps/avifgainmaputil/tonemap_command.cc
+++ b/apps/avifgainmaputil/tonemap_command.cc
@@ -132,9 +132,13 @@ avifResult TonemapCommand::Run() {
   if (depth == 0) {
     depth = tone_mapping_to_sdr ? 8 : decoder->image->depth;
   }
-  ImagePtr tone_mapped(
-      avifImageCreate(decoder->image->width, decoder->image->height, depth,
-                      (avifPixelFormat)arg_image_read_.pixel_format.value()));
+  avifPixelFormat pixel_format =
+      (avifPixelFormat)arg_image_read_.pixel_format.value();
+  if (pixel_format == AVIF_PIXEL_FORMAT_NONE) {
+    pixel_format = AVIF_PIXEL_FORMAT_YUV444;
+  }
+  ImagePtr tone_mapped(avifImageCreate(
+      decoder->image->width, decoder->image->height, depth, pixel_format));
   if (tone_mapped == nullptr) {
     return AVIF_RESULT_OUT_OF_MEMORY;
   }