diff --git a/CMakeLists.txt b/CMakeLists.txt
index ae35e2e737..78eb65072f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,6 +3,8 @@ cmake_minimum_required(VERSION 3.16)
 set(PROJECT_VERSION "5.22.80") # Handled by release scripts
 project(KWin VERSION ${PROJECT_VERSION})
 
+set(CMAKE_C_STANDARD 99)
+
 set(QT_MIN_VERSION "5.15.0")
 set(KF5_MIN_VERSION "5.82")