diff --git a/CMakeLists.txt b/CMakeLists.txt
index c1909bf7..f267fdb2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,7 +18,6 @@ if(EMSCRIPTEN)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${LOVR_EMSCRIPTEN_FLAGS}")
 elseif(UNIX)
   find_package(PkgConfig REQUIRED)
-  add_definitions(-D_XOPEN_SOURCE=600)
 endif()
 
 # PhysicsFS