diff --git a/synfig-core/src/modules/mod_ffmpeg/CMakeLists.txt b/synfig-core/src/modules/mod_ffmpeg/CMakeLists.txt
index 519d7a9..c87b667 100644
--- a/synfig-core/src/modules/mod_ffmpeg/CMakeLists.txt
+++ b/synfig-core/src/modules/mod_ffmpeg/CMakeLists.txt
@@ -1,5 +1,10 @@
 add_library(mod_ffmpeg MODULE "")
 
+if (UNIX)
+	add_definitions(-DHAVE_FORK -DHAVE_PIPE -DHAVE_WAITPID)
+	add_definitions(-DHAVE_SYS_WAIT_H)
+endif (UNIX)
+
 target_sources(mod_ffmpeg
     PUBLIC
         "${CMAKE_CURRENT_LIST_DIR}/main.cpp"