diff --git a/Makefile.am b/Makefile.am
index 663b55ee..a0de6f56 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -282,7 +282,7 @@ endif
 
 
 if AIX
-libuv_la_CFLAGS += -D_ALL_SOURCE -D_XOPEN_SOURCE=500 -D_LINUX_SOURCE_COMPAT
+libuv_la_CFLAGS += -D_ALL_SOURCE -D_XOPEN_SOURCE=500 -D_LINUX_SOURCE_COMPAT -D_THREAD_SAFE
 include_HEADERS += include/uv-aix.h
 libuv_la_SOURCES += src/unix/aix.c
 endif
diff --git a/uv.gyp b/uv.gyp
index cd945b18..a12753a9 100644
--- a/uv.gyp
+++ b/uv.gyp
@@ -241,6 +241,7 @@
             '_ALL_SOURCE',
             '_XOPEN_SOURCE=500',
             '_LINUX_SOURCE_COMPAT',
+            '_THREAD_SAFE',
           ],
           'link_settings': {
             'libraries': [