diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index 53ca4ad..3fc0165 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -2367,13 +2367,20 @@
                                     struct aom_write_bit_buffer *wb) {
   const int coded_width = cm->superres_upscaled_width - 1;
   const int coded_height = cm->superres_upscaled_height - 1;
+  const SequenceHeader *seq_params = cm->seq_params;
 
   if (frame_size_override) {
-    const SequenceHeader *seq_params = cm->seq_params;
     int num_bits_width = seq_params->num_bits_width;
     int num_bits_height = seq_params->num_bits_height;
     aom_wb_write_literal(wb, coded_width, num_bits_width);
     aom_wb_write_literal(wb, coded_height, num_bits_height);
+  } else {
+    if (cm->superres_upscaled_width != seq_params->max_frame_width ||
+        cm->superres_upscaled_height != seq_params->max_frame_height) {
+      aom_internal_error(cm->error, AOM_CODEC_UNSUP_BITSTREAM,
+                         "Frame dimensions are different from the maximum "
+                         "values when frame_size_override_flag is 0");
+    }
   }
 
   write_superres_scale(cm, wb);
@@ -2977,10 +2984,7 @@
 
   int frame_size_override_flag = 0;
 
-  if (seq_params->reduced_still_picture_hdr) {
-    assert(cm->superres_upscaled_width == seq_params->max_frame_width &&
-           cm->superres_upscaled_height == seq_params->max_frame_height);
-  } else {
+  if (!seq_params->reduced_still_picture_hdr) {
     if (seq_params->frame_id_numbers_present_flag) {
       int frame_id_len = seq_params->frame_id_length;
       aom_wb_write_literal(wb, cm->current_frame_id, frame_id_len);
diff --git a/test/forced_max_frame_width_height_test.cc b/test/forced_max_frame_width_height_test.cc
index 5211d66..d5bbdf2 100644
--- a/test/forced_max_frame_width_height_test.cc
+++ b/test/forced_max_frame_width_height_test.cc
@@ -277,4 +277,37 @@
   EXPECT_EQ(AOM_CODEC_OK, aom_codec_destroy(&enc));
 }
 
+// A regression test for bug 555350218.
+TEST(EncodeForcedMaxFrameWidthHeight, ReducedStillPictureHeader) {
+  constexpr size_t kImageDataSize = 128 * 128 + 2 * 64 * 64;
+  std::unique_ptr<unsigned char[]> img_data(new unsigned char[kImageDataSize]);
+  ASSERT_NE(img_data, nullptr);
+  memset(img_data.get(), 128, kImageDataSize);
+  aom_image_t img;
+  EXPECT_EQ(&img,
+            aom_img_wrap(&img, AOM_IMG_FMT_I420, 128, 128, 1, img_data.get()));
+
+  aom_codec_iface_t *iface = aom_codec_av1_cx();
+  aom_codec_enc_cfg_t cfg;
+  EXPECT_EQ(AOM_CODEC_OK,
+            aom_codec_enc_config_default(iface, &cfg, AOM_USAGE_REALTIME));
+  cfg.g_w = 128;
+  cfg.g_h = 128;
+  cfg.g_limit = 1;
+
+  aom_codec_ctx_t enc;
+
+  cfg.g_forced_max_frame_width = 128;
+  cfg.g_forced_max_frame_height = 128;
+  EXPECT_EQ(AOM_CODEC_OK, aom_codec_enc_init(&enc, iface, &cfg, 0));
+  EXPECT_EQ(AOM_CODEC_OK, aom_codec_encode(&enc, &img, 0, 1, 0));
+  EXPECT_EQ(AOM_CODEC_OK, aom_codec_destroy(&enc));
+
+  cfg.g_forced_max_frame_width = 256;
+  cfg.g_forced_max_frame_height = 256;
+  EXPECT_EQ(AOM_CODEC_OK, aom_codec_enc_init(&enc, iface, &cfg, 0));
+  EXPECT_NE(AOM_CODEC_OK, aom_codec_encode(&enc, &img, 0, 1, 0));
+  EXPECT_EQ(AOM_CODEC_OK, aom_codec_destroy(&enc));
+}
+
 }  // namespace