diff --git a/signature.h b/signature.h
index a052df8..239ee3e 100644
--- a/signature.h
+++ b/signature.h
@@ -21,7 +21,9 @@
 /* signature checking result codes */
 #define SIGNATURE_VALID		0
 #define SIGNATURE_INVALID	1
-#define CANT_CHECK_SIGNATURE	2
+#define CANT_ALLOCATE_COPY	2
+#define CANT_CHECK_SIGNATURE	3
 
 extern const struct tok signature_check_values[];
-extern int signature_verify(netdissect_options *, const u_char *, u_int, u_char *);
+extern int signature_verify(netdissect_options *, const u_char *, u_int,
+                            const u_char *, void (*)(void *), const void *);