cannot alter inherited constraint “…” on relation “…”

SQLSTATE 55000 condition object_not_in_prerequisite_state class 55 — Object Not In Prerequisite State severity ERROR

Reproduced & verified on PostgreSQL 14.23, 15.18, 16.14, 17.10 and 18.4 — identical message on every version.

Last reviewed 4 Jun 2026 · Reproduced live with the SQL on this page.

Symptoms

A statement failed with SQLSTATE 55000 (object_not_in_prerequisite_state), reported at severity ERROR. This is a Object Not In Prerequisite State condition: PostgreSQL emits the message cannot alter inherited constraint "…" on relation "…".

The client receives SQLSTATE 55000 (object not in prerequisite state).
The operation is rejected at ERROR level; the statement does not complete.

What the server log shows

ERROR:  cannot alter inherited constraint "…" on relation "…"

Why PostgreSQL raises this

Class 55 (Object Not In Prerequisite State) is raised when an object exists but is not in a state that allows the requested operation right now.

As described in PostgreSQL’s Appendix A PostgreSQL Error Codes, SQLSTATE 55000 carries the condition name object_not_in_prerequisite_state in class Object Not In Prerequisite State. (Paraphrased — see the linked reference for the exact wording.)

Common causes

The object is locked, in use, or being modified by another session.
A required precondition (e.g. an index, a prepared state) is not met.
The operation cannot run while the object is in its current state.

How to fix it

Wait for the conflicting session/operation to finish, then retry.
Establish the missing precondition before retrying.
Check for blocking locks with pg_locks.

Version applicability

This message text is present in PostgreSQL 18, 19. It was introduced around PostgreSQL 18; earlier releases do not emit this exact text.

Related & next steps

Reference: PostgreSQL Appendix A PostgreSQL Error Codes.