diff --git a/esphome/components/web_server_idf/web_server_idf.cpp b/esphome/components/web_server_idf/web_server_idf.cpp
index 9478e4748c..d2447681f5 100644
--- a/esphome/components/web_server_idf/web_server_idf.cpp
+++ b/esphome/components/web_server_idf/web_server_idf.cpp
@@ -37,6 +37,15 @@ namespace web_server_idf {
 
 static const char *const TAG = "web_server_idf";
 
+// Global instance to avoid guard variable (saves 8 bytes)
+// This is initialized at program startup before any threads
+namespace {
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DefaultHeaders default_headers_instance;
+}  // namespace
+
+DefaultHeaders &DefaultHeaders::Instance() { return default_headers_instance; }
+
 void AsyncWebServer::end() {
   if (this->server_) {
     httpd_stop(this->server_);
diff --git a/esphome/components/web_server_idf/web_server_idf.h b/esphome/components/web_server_idf/web_server_idf.h
index 8de25c8e96..e8e40ef9b0 100644
--- a/esphome/components/web_server_idf/web_server_idf.h
+++ b/esphome/components/web_server_idf/web_server_idf.h
@@ -328,10 +328,7 @@ class DefaultHeaders {
   void addHeader(const char *name, const char *value) { this->headers_.emplace_back(name, value); }
 
   // NOLINTNEXTLINE(readability-identifier-naming)
-  static DefaultHeaders &Instance() {
-    static DefaultHeaders instance;
-    return instance;
-  }
+  static DefaultHeaders &Instance();
 
  protected:
   std::vector<std::pair<std::string, std::string>> headers_;