diff --git a/main.h b/main.h
index 846fceda..7f7d5de1 100644
--- a/main.h
+++ b/main.h
@@ -86,7 +86,7 @@ void config_x25();
 void trans_x25();
 int upper_digit(int number);
 int lower_digit(int number);
-void update_rs(unsigned char parity[32], unsigned char c);
+extern void update_rs(unsigned char parity[32], unsigned char c);
 void write_little_endian(unsigned int word, int num_bytes, FILE *wav_file);
 static int init_rf();
 extern int Encode_8b10b[][256];