diff --git a/src/lj_cdata.c b/src/lj_cdata.c
index 04875fd6..164671fe 100644
--- a/src/lj_cdata.c
+++ b/src/lj_cdata.c
@@ -125,16 +125,16 @@ collect_attrib:
   integer_key:
     if (ctype_ispointer(ct->info)) {
       CTSize sz = lj_ctype_size(cts, ctype_cid(ct->info));  /* Element size. */
-      if (sz != CTSIZE_INVALID) {
-	if (ctype_isptr(ct->info)) {
-	  p = (uint8_t *)cdata_getptr(p, ct->size);
-	} else if ((ct->info & (CTF_VECTOR|CTF_COMPLEX))) {
-	  if ((ct->info & CTF_COMPLEX)) idx &= 1;
-	  *qual |= CTF_CONST;  /* Valarray elements are constant. */
-	}
-	*pp = p + idx*(int32_t)sz;
-	return ct;
+      if (sz == CTSIZE_INVALID)
+	lj_err_caller(cts->L, LJ_ERR_FFI_INVSIZE);
+      if (ctype_isptr(ct->info)) {
+	p = (uint8_t *)cdata_getptr(p, ct->size);
+      } else if ((ct->info & (CTF_VECTOR|CTF_COMPLEX))) {
+	if ((ct->info & CTF_COMPLEX)) idx &= 1;
+	*qual |= CTF_CONST;  /* Valarray elements are constant. */
       }
+      *pp = p + idx*(int32_t)sz;
+      return ct;
     }
   } else if (tviscdata(key)) {  /* Integer cdata key. */
     GCcdata *cdk = cdataV(key);