diff --git a/common.h b/common.h
index 31a0014..8166a71 100644
--- a/common.h
+++ b/common.h
@@ -35,12 +35,13 @@
 #define SEM_WRITE_END "/sem_write_end_01527193"
 
 #define MAX_ITEMS 16
+#define CIRC_BUF_SIZE 17
 
 struct circ_buf {
 	int quit;
 	int head;
 	int tail;
-	int data[MAX_ITEMS+1];
+	int data[CIRC_BUF_SIZE];
 };
 
 #endif /* ifndef COMMON_H */