diff --git a/include/jtag/part.h b/include/jtag/part.h
index 917200f1..92b942f9 100644
--- a/include/jtag/part.h
+++ b/include/jtag/part.h
@@ -47,7 +47,7 @@ struct part {
 
 part *part_alloc( void );
 void part_free( part *p );
-part *read_part( FILE *f );
+part *read_part( FILE *f, const tap_register *idr );
 instruction *part_find_instruction( part *p, const char *iname );
 void part_set_signal( part *p, const char *pname, int out, int val );
 int part_get_signal( part *p, const char *pname );