diff --git a/rpn.c b/rpn.c
--- a/rpn.c
+++ b/rpn.c
@@ -7,10 +7,9 @@
 
 #include <stdio.h>
 
-double val;
+#include "stack.h"
 
-extern double pop(void);
-extern void push(double);
+double val;
 
 extern int getsym(void);
 
diff --git a/stack.c b/stack.c
--- a/stack.c
+++ b/stack.c
@@ -5,6 +5,8 @@
  * Licensed under the Open Software License version 2.1
  */
 
+#include "stack.h"
+
 #define N	8
 
 static double stack[N];