diff --git a/modules/http_server_simple/http_server_simple.cpp b/modules/http_server_simple/http_server_simple.cpp
index fcb64adbb..9cf4faa95 100644
--- a/modules/http_server_simple/http_server_simple.cpp
+++ b/modules/http_server_simple/http_server_simple.cpp
@@ -288,7 +288,7 @@ void HTTPServerConnection::send_file(Ref<WebServerRequest> request, const String
 
 	if (!custom_headers.has("Content-Type")) {
 		String ctype;
-		String req_ext = p_file_path.get_extension();
+		StringName req_ext = p_file_path.get_extension().to_lower();
 
 		if (_http_server->mimes.has(req_ext)) {
 			ctype = _http_server->mimes[req_ext];
diff --git a/modules/http_server_simple/http_server_simple.h b/modules/http_server_simple/http_server_simple.h
index 0448f099a..150bc5d3d 100644
--- a/modules/http_server_simple/http_server_simple.h
+++ b/modules/http_server_simple/http_server_simple.h
@@ -110,7 +110,7 @@ public:
 
 	uint64_t max_request_size;
 
-	RBMap<String, String> mimes;
+	RBMap<StringName, String> mimes;
 
 	Ref<X509Certificate> cert;