diff --git a/CMakeLists.txt b/CMakeLists.txt
index 847adc7c..d3b35c2f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -109,12 +109,12 @@ if(NOT WIN32)
     CHECK_SYMBOL_EXISTS(posix_memalign stdlib.h HAVE_POSIX_MEMALIGN_DEFAULT)
     IF(NOT HAVE_POSIX_MEMALIGN_DEFAULT)
         SET(OLD_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
-        SET(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700")
+        SET(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -D_POSIX_C_SOURCE=200112L -D_XOPEN_SOURCE=500")
         CHECK_SYMBOL_EXISTS(posix_memalign stdlib.h HAVE_POSIX_MEMALIGN_POSIX)
         IF(NOT HAVE_POSIX_MEMALIGN_POSIX)
             SET(CMAKE_REQUIRED_FLAGS ${OLD_REQUIRED_FLAGS})
         ELSE()
-            ADD_DEFINITIONS(-D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=700)
+            ADD_DEFINITIONS(-D_POSIX_C_SOURCE=200112L -D_XOPEN_SOURCE=500)
         ENDIF()
     ENDIF()
     UNSET(OLD_REQUIRED_FLAGS)