diff --git a/CMakeLists.txt b/CMakeLists.txt
index c7b201d..199cf3a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -82,7 +82,7 @@ if( NOT IMLIB_BUILD_WITH_X )
   message( FATAL_ERROR "Imlib is not built with X support" )
 endif( NOT IMLIB_BUILD_WITH_X )
 
-add_definitions( -D_POSIX_C_SOURCE=200809L -D_BSD_SOURCE )
+add_definitions( -D_POSIX_C_SOURCE=200809L -D_BSD_SOURCE -D_DEFAULT_SOURCE )
 
 include_directories( ${PROJECT_BINARY_DIR}
                      src