diff --git a/test/BUILD.gn b/test/BUILD.gn
index 49ab773ea2..85694eb1c2 100644
--- a/test/BUILD.gn
+++ b/test/BUILD.gn
@@ -456,6 +456,7 @@ rtc_library("video_test_support") {
     "../rtc_base:criticalsection",
     "../rtc_base:logging",
     "../rtc_base:rtc_event",
+    "../rtc_base:stringutils",
     "../rtc_base/system:file_wrapper",
   ]
   absl_deps = [ "//third_party/abseil-cpp/absl/types:optional" ]
diff --git a/test/testsupport/frame_reader.h b/test/testsupport/frame_reader.h
index ac399655df..d2a3b4b064 100644
--- a/test/testsupport/frame_reader.h
+++ b/test/testsupport/frame_reader.h
@@ -110,7 +110,7 @@ class Y4mFrameReaderImpl : public YuvFrameReaderImpl {
 
  private:
   // Buffer that is used to read file and frame headers.
-  uint8_t* buffer_;
+  char* buffer_;
 };
 
 }  // namespace test
diff --git a/test/testsupport/y4m_frame_reader.cc b/test/testsupport/y4m_frame_reader.cc
index 6c34a2dd3e..0faa024141 100644
--- a/test/testsupport/y4m_frame_reader.cc
+++ b/test/testsupport/y4m_frame_reader.cc
@@ -15,6 +15,7 @@
 #include "api/scoped_refptr.h"
 #include "api/video/i420_buffer.h"
 #include "rtc_base/logging.h"
+#include "rtc_base/strings/string_builder.h"
 #include "test/testsupport/file_utils.h"
 #include "test/testsupport/frame_reader.h"
 
@@ -22,11 +23,20 @@ namespace webrtc {
 namespace test {
 namespace {
 
-// Size of header: "YUV4MPEG2 W50 H20 F30:1 C420\n"
-const size_t kFileHeaderSize = 29;
+// Size of header: "YUV4MPEG2 WXXXXXX HXXXXXX FXXX:1 C420\n"
+// We allocate up to 6 digits for width and height and up to 3 digits for FPS.
+const size_t kFileHeaderMaxSize = 38;
+// Size of header: "YUV4MPEG2 WX HX FX:1 C420\n"
+const size_t kFileHeaderMinSize = 26;
 // Size of header: "FRAME\n"
 const size_t kFrameHeaderSize = 6;
 
+std::string GetExpectedHeaderPrefix(int width, int height) {
+  rtc::StringBuilder out;
+  out << "YUV4MPEG2 W" << width << " H" << height << " F";
+  return out.str();
+}
+
 }  // namespace
 
 Y4mFrameReaderImpl::Y4mFrameReaderImpl(std::string input_filename,
@@ -34,7 +44,7 @@ Y4mFrameReaderImpl::Y4mFrameReaderImpl(std::string input_filename,
                                        int height)
     : YuvFrameReaderImpl(input_filename, width, height) {
   frame_length_in_bytes_ += kFrameHeaderSize;
-  buffer_ = new uint8_t[kFileHeaderSize];
+  buffer_ = new char[kFileHeaderMaxSize];
 }
 Y4mFrameReaderImpl::~Y4mFrameReaderImpl() {
   delete[] buffer_;
@@ -48,28 +58,35 @@ bool Y4mFrameReaderImpl::Init() {
   }
   input_file_ = fopen(input_filename_.c_str(), "rb");
   if (input_file_ == nullptr) {
-    RTC_LOG(LS_ERROR) << "Couldn't open input file: "
-                      << input_filename_.c_str();
+    RTC_LOG(LS_ERROR) << "Couldn't open input file: " << input_filename_;
     return false;
   }
   size_t source_file_size = GetFileSize(input_filename_);
   if (source_file_size <= 0u) {
-    RTC_LOG(LS_ERROR) << "Input file " << input_filename_.c_str()
-                      << " is empty.";
+    RTC_LOG(LS_ERROR) << "Input file " << input_filename_ << " is empty.";
     return false;
   }
-  if (fread(buffer_, 1, kFileHeaderSize, input_file_) < kFileHeaderSize) {
+  char* c_file_header = fgets(buffer_, kFileHeaderMaxSize, input_file_);
+  std::string file_header(c_file_header);
+  if (file_header.size() < kFileHeaderMinSize) {
     RTC_LOG(LS_ERROR) << "Couldn't read Y4M header from input file: "
-                      << input_filename_.c_str();
+                      << input_filename_;
+    return false;
+  }
+  if (file_header.find(GetExpectedHeaderPrefix(input_width_, input_height_)) !=
+      0) {
+    RTC_LOG(LS_ERROR) << "Couldn't read Y4M file: " << input_filename_
+                      << ". Input file has different resolution, expected: "
+                      << GetExpectedHeaderPrefix(input_width_, input_height_)
+                      << "[0-9]?:1 C420; got: " << file_header;
     return false;
   }
 
-  number_of_frames_ = static_cast<int>((source_file_size - kFileHeaderSize) /
+  number_of_frames_ = static_cast<int>((source_file_size - file_header.size()) /
                                        frame_length_in_bytes_);
 
   if (number_of_frames_ == 0) {
-    RTC_LOG(LS_ERROR) << "Input file " << input_filename_.c_str()
-                      << " is too small.";
+    RTC_LOG(LS_ERROR) << "Input file " << input_filename_ << " is too small.";
   }
   return true;
 }
@@ -82,7 +99,7 @@ rtc::scoped_refptr<I420Buffer> Y4mFrameReaderImpl::ReadFrame() {
   if (fread(buffer_, 1, kFrameHeaderSize, input_file_) < kFrameHeaderSize &&
       ferror(input_file_)) {
     RTC_LOG(LS_ERROR) << "Couldn't read frame header from input file: "
-                      << input_filename_.c_str();
+                      << input_filename_;
     return nullptr;
   }
   return YuvFrameReaderImpl::ReadFrame();
diff --git a/test/testsupport/y4m_frame_reader_unittest.cc b/test/testsupport/y4m_frame_reader_unittest.cc
index f7e2651ec9..219ec1bbe3 100644
--- a/test/testsupport/y4m_frame_reader_unittest.cc
+++ b/test/testsupport/y4m_frame_reader_unittest.cc
@@ -26,7 +26,7 @@ namespace webrtc {
 namespace test {
 namespace {
 
-const absl::string_view kFileHeader = "YUV4MPEG2 W50 H20 F30:1 C420\n";
+const absl::string_view kFileHeader = "YUV4MPEG2 W2 H2 F30:1 C420\n";
 const absl::string_view kFrameHeader = "FRAME\n";
 const absl::string_view kInputVideoContents = "abcdef";
 
@@ -90,5 +90,15 @@ TEST_F(Y4mFrameReaderTest, ReadFrameUninitialized) {
   EXPECT_FALSE(file_reader.ReadFrame());
 }
 
+TEST_F(Y4mFrameReaderTest, ReadFrameDifferentWidth) {
+  Y4mFrameReaderImpl file_reader(temp_filename_, kFrameWidth + 1, kFrameHeight);
+  EXPECT_FALSE(file_reader.Init());
+}
+
+TEST_F(Y4mFrameReaderTest, ReadFrameDifferentHeight) {
+  Y4mFrameReaderImpl file_reader(temp_filename_, kFrameWidth, kFrameHeight + 1);
+  EXPECT_FALSE(file_reader.Init());
+}
+
 }  // namespace test
 }  // namespace webrtc