diff --git a/cont.c b/cont.c
index 839b6703a9..4ca1279d02 100644
--- a/cont.c
+++ b/cont.c
@@ -49,7 +49,7 @@
 static long pagesize;
 
  #if SIZEOF_VOIDP==8
-  #define FIBER_MACHINE_STACK_ALLOCATION_SIZE  (0x100000)
+  #define FIBER_MACHINE_STACK_ALLOCATION_SIZE  (0x20000)
  #else
   #define FIBER_MACHINE_STACK_ALLOCATION_SIZE  (0x10000)
  #endif