diff --git a/ctf_encoder.c b/ctf_encoder.c
index 3763415..825cfa2 100644
--- a/ctf_encoder.c
+++ b/ctf_encoder.c
@@ -138,7 +138,7 @@ static int subroutine_type__encode(struct tag *self, uint16_t core_id,
 	int64_t position;
 	struct ftype *ftype = tag__ftype(self);
 	int ctf_id = ctf__add_function_type(ctf, self->type, ftype->nr_parms,
-					    &position);
+					    ftype->unspec_parms, &position);
 
 	if (ctf_id < 0 || tag__check_id_drift(self, core_id, ctf_id))
 		return -1;
diff --git a/ctf_loader.c b/ctf_loader.c
index 6734d0a..5d071fe 100644
--- a/ctf_loader.c
+++ b/ctf_loader.c
@@ -469,11 +469,17 @@ static int create_new_subroutine_type(struct ctf_state *sp, void *ptr,
 	INIT_LIST_HEAD(&self->lexblock.tags);
 
 	for (i = 0; i < vlen; i++) {
-		struct parameter *p = tag__alloc(sizeof(*p));
+		uint16_t type = ctf__get16(sp->ctf, &args[i]);
 
-		p->tag.tag  = DW_TAG_formal_parameter;
-		p->tag.type = ctf__get16(sp->ctf, &args[i]);
-		ftype__add_parameter(&self->proto, p);
+		if (type == 0)
+			self->proto.unspec_parms = 1;
+		else {
+			struct parameter *p = tag__alloc(sizeof(*p));
+
+			p->tag.tag  = DW_TAG_formal_parameter;
+			p->tag.type = ctf__get16(sp->ctf, &args[i]);
+			ftype__add_parameter(&self->proto, p);
+		}
 	}
 
 	vlen *= sizeof(*args);
diff --git a/libctf.c b/libctf.c
index 85378e8..e8fd2c8 100644
--- a/libctf.c
+++ b/libctf.c
@@ -297,10 +297,10 @@ void ctf__add_parameter(struct ctf *self, uint16_t type, int64_t *position)
 }
 
 int ctf__add_function_type(struct ctf *self, uint16_t type, uint16_t nr_parms,
-			   int64_t *position)
+			   bool varargs, int64_t *position)
 {
 	struct ctf_short_type t;
-	int len = sizeof(uint16_t) * nr_parms;
+	int len = sizeof(uint16_t) * (nr_parms + !!varargs);
 
 	/*
 	 * Round up to next multiple of 4 to maintain 32-bit alignment.
@@ -309,11 +309,18 @@ int ctf__add_function_type(struct ctf *self, uint16_t type, uint16_t nr_parms,
 		len += 0x2;
 
 	t.ctf_name = 0;
-	t.ctf_info = CTF_INFO_ENCODE(CTF_TYPE_KIND_FUNC, nr_parms, 0);
+	t.ctf_info = CTF_INFO_ENCODE(CTF_TYPE_KIND_FUNC,
+				     nr_parms + !!varargs, 0);
 	t.ctf_type = type;
 
 	gobuffer__add(&self->types, &t, sizeof(t));
 	*position = gobuffer__allocate(&self->types, len);
+	if (varargs) {
+		unsigned int pos = *position + (nr_parms * sizeof(uint16_t));
+		uint16_t *end_of_args = gobuffer__ptr(&self->types, pos);
+		*end_of_args = 0;
+	}
+
 	return ++self->type_index;
 }
 
diff --git a/libctf.h b/libctf.h
index 9f168fc..62c21b8 100644
--- a/libctf.h
+++ b/libctf.h
@@ -30,7 +30,7 @@ int ctf__add_array(struct ctf *self, uint16_t type, uint16_t index_type,
 		   uint32_t nelems);
 void ctf__add_parameter(struct ctf *self, uint16_t type, int64_t *position);
 int ctf__add_function_type(struct ctf *self, uint16_t type,
-			   uint16_t nr_parameters, int64_t *position);
+			   uint16_t nr_parms, bool varargs, int64_t *position);
 int ctf__add_enumeration_type(struct ctf *self, uint32_t name,
 			      uint16_t nr_entries, int64_t *position);
 void ctf__add_enumerator(struct ctf *self, uint32_t name, uint32_t value,