diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3f0d4807a..3cf72db20 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -455,9 +455,10 @@ target_compile_options(openmc PRIVATE ${cxxflags})
 target_include_directories(openmc PRIVATE ${CMAKE_BINARY_DIR}/include)
 target_link_libraries(openmc libopenmc)
 
-# Ensure C++14 standard is used
+# Ensure C++14 standard is used and turn off GNU extensions
 target_compile_features(openmc PUBLIC cxx_std_14)
 target_compile_features(libopenmc PUBLIC cxx_std_14)
+set_target_properties(openmc libopenmc PROPERTIES CXX_EXTENSIONS OFF)
 
 #===============================================================================
 # Python package