diff --git a/epan/dissectors/packet-per.c b/epan/dissectors/packet-per.c
index 92bba5b642..a023dba5c9 100644
--- a/epan/dissectors/packet-per.c
+++ b/epan/dissectors/packet-per.c
@@ -1839,7 +1839,7 @@ dissect_per_External(tvbuff_t *tvb _U_, int offset _U_, asn1_ctx_t *actx _U_, pr
 
 
 guint32 
-dissect_per_external_type(tvbuff_t *tvb, guint32 offset, asn1_ctx_t *actx, proto_tree *tree, int hf_index, per_type_fn type_cb)
+dissect_per_external_type(tvbuff_t *tvb _U_, guint32 offset, asn1_ctx_t *actx, proto_tree *tree _U_, int hf_index _U_, per_type_fn type_cb)
 {
   asn1_ctx_clean_external(actx);
   actx->external.per.type_cb = type_cb;