diff --git a/demos/state_machine/state_machine.c b/demos/state_machine/state_machine.c
index 0140fbca70..9cede29350 100644
--- a/demos/state_machine/state_machine.c
+++ b/demos/state_machine/state_machine.c
@@ -347,7 +347,7 @@ int main(int argc,char **argv)
 	    }
 
 	/* FIXME: we should only extract if stdout is ready */
-	n=SSLStateMachine_read_extract(pMachine,buf,n);
+	n=SSLStateMachine_read_extract(pMachine,buf,sizeof buf);
 	if(n < 0)
 	    {
 	    SSLStateMachine_print_error(pMachine,"read extract failed");