diff --git a/CMakeLists.txt b/CMakeLists.txt
index a7ba9e91..148d0e68 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -325,7 +325,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "OS400")
 endif()
 
 if(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
-  list(APPEND uv_defines __EXTENSIONS__ _XOPEN_SOURCE=500)
+  list(APPEND uv_defines __EXTENSIONS__ _XOPEN_SOURCE=500 _REENTRANT)
   list(APPEND uv_libraries kstat nsl sendfile socket)
   list(APPEND uv_sources
        src/unix/no-proctitle.c