diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8f0eba6a..2378c4ca 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -183,7 +183,7 @@ ELSEIF (CMAKE_SYSTEM_NAME STREQUAL "Linux")
 ELSEIF (CMAKE_SYSTEM_NAME STREQUAL "SunOS")
 	LIST (APPEND SYSFLAGS -D__EXTENSIONS__ -D_REENTRANT -D_XOPEN_SOURCE=600)
 ELSEIF (CMAKE_SYSTEM_NAME STREQUAL "AIX")
-	LIST (APPEND SYSFLAGS -D_ALL_SOURCE -D_XOPEN_SOURCE=600)
+	LIST (APPEND SYSFLAGS -D_ALL_SOURCE -D_XOPEN_SOURCE=600 -D_USE_IRS)
 ELSEIF (CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
 	# Don't define _XOPEN_SOURCE on FreeBSD, it actually reduces visibility instead of increasing it
 ELSEIF (WIN32)