diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5edd305185..47aa10fc26 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -420,6 +420,9 @@ if(NOT MSVC)
 		add_definitions(-D_XOPEN_SOURCE=700)
 		add_definitions(-D_XOPEN_SOURCE_EXTENDED -D__BSD_VISIBLE=1 -D_BSD_SOURCE -D_DEFAULT_SOURCE)
 		add_definitions(-D_LARGEFILE64_SOURCE=1 -D_FILE_OFFSET_BITS=64)
+		if(${CMAKE_SYSTEM_NAME} STREQUAL "NetBSD")
+			add_definitions(-D_NETBSD_SOURCE)
+		endif()
 	elseif(ANDROID)
 		add_definitions(-fsigned-char)
 	endif()