Document cardinality violation status codes
diff --git a/doc/statuscodes.md b/doc/statuscodes.md
index 84258c8..c918f9e 100644
--- a/doc/statuscodes.md
+++ b/doc/statuscodes.md
@@ -21,6 +21,8 @@
| Flow-control protocol violation | INTERNAL | Both |
| Error parsing returned status | UNKNOWN | Client |
| Incorrect Auth metadata ( Credentials failed to get metadata, Incompatible credentials set on channel and call, Invalid host set in `:authority` metadata, etc.) | UNAUTHENTICATED | Both |
+| Request cardinality violation (method requires exactly one request but client sent some other number of requests) | UNIMPLEMENTED | Server|
+| Response cardinality violation (method requires exactly one response but server sent some other number of responses) | UNIMPLEMENTED | Client|
| Error parsing response proto | INTERNAL | Client|
| Error parsing request proto | INTERNAL | Server|
