diff --git a/src/libmawk/vio_fifo.h b/src/libmawk/vio_fifo.h
index f170c22..a2d751d 100644
--- a/src/libmawk/vio_fifo.h
+++ b/src/libmawk/vio_fifo.h
@@ -14,7 +14,7 @@ typedef struct mawk_vio_fifo_s {
 	int eof_from_app;       /* 1 if there won't be more from the app or the app won't accept more data */
 } mawk_vio_fifo_t;
 
-const mawk_vio_imp_t mawk_vio_fifo_imp;
+extern const mawk_vio_imp_t mawk_vio_fifo_imp;
 
 mawk_vio_t *mawk_vio_fifo_open(mawk_state_t *MAWK, const char *name, mawk_vio_open_mode_t mode);