diff --git a/src/mime/type.go b/src/mime/type.go
index 58cc22fdb0..6115a9b87c 100644
--- a/src/mime/type.go
+++ b/src/mime/type.go
@@ -115,7 +115,8 @@ var builtinTypesLower = map[string]string{
 	".vtt":   "text/vtt; charset=utf-8",
 	".wasm":  "application/wasm",
 	".wav":   "audio/wav",
-	".webm":  "audio/webm",
+	".weba":  "audio/webm",
+	".webm":  "video/webm",
 	".webp":  "image/webp",
 	".xbl":   "text/xml; charset=utf-8",
 	".xbm":   "image/x-xbitmap",
diff --git a/src/mime/type_test.go b/src/mime/type_test.go
index f4ec8c8754..0c334356bb 100644
--- a/src/mime/type_test.go
+++ b/src/mime/type_test.go
@@ -245,7 +245,8 @@ func TestExtensionsByType2(t *testing.T) {
 		{typ: "text/vtt; charset=utf-8", want: []string{".vtt"}},
 		{typ: "application/wasm", want: []string{".wasm"}},
 		{typ: "audio/wav", want: []string{".wav"}},
-		{typ: "audio/webm", want: []string{".webm"}},
+		{typ: "audio/webm", want: []string{".weba"}},
+		{typ: "video/webm", want: []string{".webm"}},
 		{typ: "image/webp", want: []string{".webp"}},
 		{typ: "text/xml; charset=utf-8", want: []string{".xbl", ".xml", ".xsl"}},
 		{typ: "image/x-xbitmap", want: []string{".xbm"}},