diff --git a/src/mzscheme/src/thread.c b/src/mzscheme/src/thread.c
index 079e214de6..fde5eed099 100644
--- a/src/mzscheme/src/thread.c
+++ b/src/mzscheme/src/thread.c
@@ -5180,8 +5180,8 @@ typedef struct Evt {
   int can_redirect;
 } Evt;
 
-static int evts_array_size;
-static Evt **evts;
+static THREAD_LOCAL int evts_array_size;
+static THREAD_LOCAL Evt **evts;
 
 void scheme_add_evt(Scheme_Type type,
 		    Scheme_Ready_Fun ready,