--- a/src/isapnp_main.c
+++ b/src/isapnp_main.c
@@ -1153,7 +1153,7 @@
 	return 0;
 }
 
-unsigned char serial_identifier[NUM_CARDS+1][IDENT_LEN];
+extern unsigned char serial_identifier[NUM_CARDS+1][IDENT_LEN];
 static char *boardid[NUM_CARDS+1];
 static unsigned long serno[NUM_CARDS+1];
 
--- a/src/isapnp_main.l
+++ b/src/isapnp_main.l
@@ -363,7 +363,7 @@
 	return 0;
 }
 
-unsigned char serial_identifier[NUM_CARDS+1][IDENT_LEN];
+extern unsigned char serial_identifier[NUM_CARDS+1][IDENT_LEN];
 static char *boardid[NUM_CARDS+1];
 static unsigned long serno[NUM_CARDS+1];