diff --git a/CMakeLists.txt b/CMakeLists.txt
index 74043f08..f9191207 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -179,6 +179,7 @@ if (NOT NO_DEBUG)
 endif (NOT NO_DEBUG)
 
 if (WIN32)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_POSIX_C_SOURCE=1")
     set(CMAKE_VALA_FLAGS "${CMAKE_VALA_FLAGS} --define=_WIN32")
 endif(WIN32)