diff --git a/libctf/ctf-dedup.c b/libctf/ctf-dedup.c
index c46f69e..6297c45 100644
--- a/libctf/ctf-dedup.c
+++ b/libctf/ctf-dedup.c
@@ -2306,6 +2306,10 @@
   ctf_id_t one_type;
   ctf_id_t two_type;
 
+  /* Inputs are always equal to themselves.  */
+  if (one == two)
+    return 0;
+
   one_gid = ctf_dynhash_lookup (d->cd_output_first_gid, one_hval);
   two_gid = ctf_dynhash_lookup (d->cd_output_first_gid, two_hval);