Index: b/g10/gpg.c
===================================================================
--- b/g10/gpg.c
+++ b/g10/gpg.c
@@ -2081,6 +2081,128 @@
   return configname;
 }
 
+strlist_t
+check_user_ids (strlist_t s, const char *option,
+                int warn_possibly_ambiguous, int die_if_not_found)
+{
+  strlist_t t;
+  KEYDB_HANDLE hd = NULL;
+  int die = 0;
+  PKT_public_key *pk;
+  char fingerprint_bin[MAX_FINGERPRINT_LEN];
+  size_t fingerprint_bin_len = sizeof (fingerprint_bin);
+  char fingerprint[2 * MAX_FINGERPRINT_LEN + 1];
+  strlist_t s2 = NULL;
+
+  if (! s)
+    return NULL;
+
+  for (t = s; t; t = t->next)
+    {
+      gpg_error_t err;
+      KEYDB_SEARCH_DESC desc;
+      KBNODE kb;
+
+      err = classify_user_id (t->d, &desc, 1);
+      if (err)
+        {
+          log_error (_("Invalid value ('%s') passed to %s.\n"),
+                     t->d, option);
+          die = 1;
+          continue;
+        }
+
+      if (warn_possibly_ambiguous
+          && ! (desc.mode == KEYDB_SEARCH_MODE_LONG_KID
+                || desc.mode == KEYDB_SEARCH_MODE_FPR16
+                || desc.mode == KEYDB_SEARCH_MODE_FPR20
+                || desc.mode == KEYDB_SEARCH_MODE_FPR))
+        log_info (_("Warning: value '%s' for %s"
+                    " should be a long keyid or a fingerprint.\n"),
+                  t->d, option);
+
+      if (! hd)
+        hd = keydb_new ();
+      else
+        keydb_search_reset (hd);
+
+      err = keydb_search (hd, &desc, 1, NULL);
+      if (gpg_err_code (err) == GPG_ERR_NOT_FOUND)
+        {
+          if (die_if_not_found)
+            {
+              log_error (_("no such key corresponding to %s (passed to %s)\n"),
+                         t->d, option);
+              die = 1;
+            }
+          continue;
+        }
+      if (err)
+        {
+          log_error (_("error looking up %s in keyring: %s.\n"),
+                     t->d, gpg_strerror (err));
+          die = 1;
+          break;
+        }
+
+      err = keydb_get_keyblock (hd, &kb);
+      if (err)
+        {
+          log_error (_("error reading key block for %s: %s\n"),
+                     t->d, gpg_strerror (err));
+          die = 1;
+          continue;
+        }
+
+      pk = kb->pkt->pkt.public_key;
+      fingerprint_from_pk (pk, fingerprint_bin, &fingerprint_bin_len);
+      assert (fingerprint_bin_len == sizeof (fingerprint_bin));
+      bin2hex (fingerprint_bin, MAX_FINGERPRINT_LEN, fingerprint);
+      append_to_strlist (&s2, fingerprint);
+
+      release_kbnode (kb);
+
+      /* Continue the search.  */
+      err = keydb_search (hd, &desc, 1, NULL);
+      if (! (gpg_err_code (err) == GPG_ERR_NOT_FOUND
+             || gpg_err_code (err) == GPG_ERR_EOF))
+        {
+          char fingerprint_bin2[MAX_FINGERPRINT_LEN];
+          size_t fingerprint_bin2_len = sizeof (fingerprint_bin2);
+          char fingerprint2[2 * MAX_FINGERPRINT_LEN + 1];
+
+          log_error ("Error: the key specification '%s' is ambiguous (passed to %s).\n",
+                     t->d, option);
+          die = 1;
+
+          err = keydb_get_keyblock (hd, &kb);
+          if (err)
+            log_error (_("error reading key block for %s: %s.\n"),
+                       t->d, gpg_strerror (err));
+          else
+            {
+              pk = kb->pkt->pkt.public_key;
+              fingerprint_from_pk (pk, fingerprint_bin2, &fingerprint_bin2_len);
+              assert (fingerprint_bin2_len == sizeof (fingerprint_bin2));
+              bin2hex (fingerprint_bin2, MAX_FINGERPRINT_LEN, fingerprint2);
+
+              log_error ("'%s' matches at least: %s and %s.\n",
+                         t->d, fingerprint, fingerprint2);
+
+              release_kbnode (kb);
+            }
+        }
+    }
+
+  if (hd)
+    keydb_release (hd);
+
+  if (die)
+    g10_exit(2);
+
+  free_strlist (s);
+  return s2;
+}
 
 int
 main (int argc, char **argv)
@@ -3754,6 +3876,11 @@
           log_info (_("--encrypt-to-default-key specified, but --default-key not specified.\n"));
       }
 
+    locusr = check_user_ids (locusr, "--local-user", 1, 1);
+    remusr = check_user_ids (remusr, "--encrypt-to", 0, 1);
+    opt.def_secret_key = check_user_ids (opt.def_secret_key,
+                                         "--default-key", 1, 0);
+
     /* The command dispatcher.  */
     switch( cmd )
       {