diff --git a/third_party/blink/renderer/core/html/media/html_media_element.cc b/third_party/blink/renderer/core/html/media/html_media_element.cc
index 0ecba68e421f..e565c5c81d77 100644
--- a/third_party/blink/renderer/core/html/media/html_media_element.cc
+++ b/third_party/blink/renderer/core/html/media/html_media_element.cc
@@ -124,6 +124,7 @@
 // For BUILDFLAG(USE_STARBOARD_MEDIA)
 #include "build/build_config.h"
 #if BUILDFLAG(USE_STARBOARD_MEDIA)
+#include "base/strings/string_util.h"
 #include "starboard/media.h"
 #endif  // BUILDFLAG(USE_STARBOARD_MEDIA)
 
@@ -408,7 +409,8 @@ std::ostream& operator<<(std::ostream& stream,
 #if BUILDFLAG(USE_STARBOARD_MEDIA)
 // Checks for progressive formats served by the YouTube H5 player.
 // These formats have a mime type of "video/mp4", and lists both audio and
-// video codecs under the "codecs" parameter.
+// video codecs under the "codecs" parameter. This is not a comprehensive
+// check and may not detect all progressive formats.
 bool IsProgressiveFormat(const ContentType& content_type) {
   const String type = content_type.GetType();
   const String codecs = content_type.Parameter("codecs");
@@ -418,7 +420,7 @@ bool IsProgressiveFormat(const ContentType& content_type) {
   }
 
   Vector<String> split_codecs;
-  const String separator(", ");
+  const String separator(",");
   codecs.Split(separator, split_codecs);
   return type.Utf8() == "video/mp4" && split_codecs.size() == 2;
 }
diff --git a/third_party/blink/renderer/core/html/media/html_media_element_test.cc b/third_party/blink/renderer/core/html/media/html_media_element_test.cc
index 81841cfae1d3..c3439a87a486 100644
--- a/third_party/blink/renderer/core/html/media/html_media_element_test.cc
+++ b/third_party/blink/renderer/core/html/media/html_media_element_test.cc
@@ -1578,6 +1578,8 @@ TEST_P(HTMLMediaElementTest, CanFreezeWithMediaPlayerAttached) {
 TEST(HTMLMediaElementTest, CanHandleCobaltProgressiveSupportQueries) {
   const ContentType progressive_type(
       "video/mp4; codecs=\"avc1.42001E, mp4a.40.2\"");
+  const ContentType progressive_type_missing_whitespace(
+      "video/mp4; codecs=\"avc1.42001E,mp4a.40.2\"");
   const ContentType adaptive_video_type(
       "video/mp4; codecs=\"avc1.4d4015\"; framerate=30");
   const ContentType adaptive_audio_type(
@@ -1590,6 +1592,11 @@ TEST(HTMLMediaElementTest, CanHandleCobaltProgressiveSupportQueries) {
     // disabled.
     EXPECT_EQ(HTMLMediaElement::GetSupportsType(progressive_type),
               MIMETypeRegistry::kNotSupported);
+    // Reject progressive content types when the "codecs" parameter lacks
+    // whitespace.
+    EXPECT_EQ(
+        HTMLMediaElement::GetSupportsType(progressive_type_missing_whitespace),
+        MIMETypeRegistry::kNotSupported);
     // Continue to support adaptive content types.
     EXPECT_NE(HTMLMediaElement::GetSupportsType(adaptive_video_type),
               MIMETypeRegistry::kNotSupported);
@@ -1603,6 +1610,11 @@ TEST(HTMLMediaElementTest, CanHandleCobaltProgressiveSupportQueries) {
     // enabled.
     EXPECT_NE(HTMLMediaElement::GetSupportsType(progressive_type),
               MIMETypeRegistry::kNotSupported);
+    // Continue to accept progressive content types when the "codecs" parameter
+    // lacks whitespace.
+    EXPECT_NE(
+        HTMLMediaElement::GetSupportsType(progressive_type_missing_whitespace),
+        MIMETypeRegistry::kNotSupported);
     // Continue to support adaptive content types.
     EXPECT_NE(HTMLMediaElement::GetSupportsType(adaptive_video_type),
               MIMETypeRegistry::kNotSupported);