diff --git a/src/mcp/server/auth/provider.py b/src/mcp/server/auth/provider.py
index 957082a854..cba4dc21d1 100644
--- a/src/mcp/server/auth/provider.py
+++ b/src/mcp/server/auth/provider.py
@@ -64,6 +64,7 @@ class RegistrationError(Exception):
     "invalid_scope",
     "server_error",
     "temporarily_unavailable",
+    "invalid_target",  # RFC 8707 §2 — resource indicator mismatch
 ]