diff --git a/cmake/os/Linux.cmake b/cmake/os/Linux.cmake
index 10d3a719609cce78b5b6b5c826138aff377aec77..13fa1c3f14805eb135dabd21ce5ee2e378b5135f 100644
--- a/cmake/os/Linux.cmake
+++ b/cmake/os/Linux.cmake
@@ -22,6 +22,7 @@ INCLUDE(CheckSymbolExists)
 SET(TARGET_OS_LINUX 1)
 SET(HAVE_NPTL 1)
 SET(_GNU_SOURCE 1)
+SET(CMAKE_REQUIRED_DEFINITIONS ${CMAKE_REQUIRED_DEFINITIONS} -D_GNU_SOURCE=1)
 
 # Fix CMake (< 2.8) flags. -rdynamic exports too many symbols.
 FOREACH(LANG C CXX)