diff --git a/CMakeLists.txt b/CMakeLists.txt
index 456d98293..cbfa8dda3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -40,6 +40,7 @@ set(OT_EXTERNAL_MBEDTLS "" CACHE STRING "Specify external mbedtls library")
 option(OT_MBEDTLS_THREADING "enable mbedtls threading" OFF)
 
 add_library(ot-config INTERFACE)
+set(CMAKE_CXX_EXTENSIONS OFF)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_C_STANDARD 99)