diff --git a/src/screen.c b/src/screen.c
index 629acbc..3113604 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -36,6 +36,8 @@ static int indexX, indexY;
 static WINDOW *screen;
 static long long interval_start; /* interval start time in u sec */
 
+int nrow, ncol;
+
 char getch_screen(void)
 {
 	return (char)wgetch(screen);
diff --git a/src/screen.h b/src/screen.h
index 88bdbb3..3324fad 100644
--- a/src/screen.h
+++ b/src/screen.h
@@ -25,5 +25,5 @@ void outputDsp(unsigned char dsp);
 char getch_screen(void);
 void select_screen(void);
 
-int nrow, ncol;
+extern int nrow, ncol;