diff --git a/cmake/BuildLua.cmake b/cmake/BuildLua.cmake
index 0882104..b9e27c5 100644
--- a/cmake/BuildLua.cmake
+++ b/cmake/BuildLua.cmake
@@ -62,12 +62,11 @@ macro(build_lua LUA_VERSION)
         # with -fPIC".
         set(CFLAGS "${CFLAGS} -fPIC")
         set(CFLAGS "${CFLAGS} -DLUA_USE_DLOPEN")
+        # `io.popen()` is not supported by default, it is enabled
+        # by `LUA_USE_POSIX` flag. Required by a function `random_locale()`.
+        set(CFLAGS "${CFLAGS} -DLUA_USE_POSIX")
     endif()
 
-    # `io.popen()` is not supported by default, it is enabled
-    # by `LUA_USE_POSIX` flag. Required by a function `random_locale()`.
-    set(CFLAGS "${CFLAGS} -DLUA_USE_POSIX")
-
     include(ExternalProject)
 
     set(LUA_LIBRARY ${PROJECT_BINARY_DIR}/lua-${LUA_VERSION}/source/liblua.a)