diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -4,3 +4,6 @@
 
 rpn: rpn.o stack.o lexer.o
 	$(CC) $(CFLAGS) $^ -o $@
+	
+rpn.o lexer.o: lexer.h
+	
diff --git a/lexer.c b/lexer.c
--- a/lexer.c
+++ b/lexer.c
@@ -8,7 +8,7 @@
 #include <stdio.h>
 #include <ctype.h>
 
-extern double val;
+#include "lexer.h"
 
 int getsym(void)
 {
diff --git a/rpn.c b/rpn.c
--- a/rpn.c
+++ b/rpn.c
@@ -7,14 +7,14 @@
 
 #include <stdio.h>
 
+#include "lexer.h"
+
 double val;
 
 extern double pop(void);
 extern void push(double);
 extern void clear(void);
 
-extern int getsym(void);
-
 int main(void)
 {
 	int sym;