diff --git a/distrib/postgresql/mysql2pg.go b/distrib/postgresql/mysql2pg.go
new file mode 100644
index 000000000..528f7f028
--- /dev/null
+++ b/distrib/postgresql/mysql2pg.go
@@ -0,0 +1,398 @@
+// migrate-mysql-to-postgres copies Ergo's history data from a MySQL database
+// to a PostgreSQL database, reading connection details from an Ergo config file
+// with both databases populated in `datastore` (neither database needs `enabled: true`
+// to work.) It creates the PostgreSQL schema from scratch, then copies all data.
+//
+// WARNINGS:
+// 1. This was tested with Ergo v2.18.0 only
+// 2. It will destroy any preexisting data on the PostgreSQL side
+// 3. It should not modify any data on the MySQL side, but make a backup first anyway
+// 4. For best results, quiesce MySQL by stopping Ergo before running the migration
+//
+// Usage:
+//
+//	go run ./distrib/postgresql/mysql2pg -config /path/to/ircd.yaml
+package main
+
+import (
+	"database/sql"
+	"flag"
+	"fmt"
+	"log"
+	"net/url"
+	"os"
+
+	_ "github.com/go-sql-driver/mysql"
+	_ "github.com/jackc/pgx/v5/stdlib"
+	"gopkg.in/yaml.v2"
+)
+
+const (
+	maxTargetLength   = 64  // copied from irc/postgresql/config.go
+	latestSchema      = "2" // copied from irc/postgresql/history.go
+	latestMinorSchema = "2"
+	batchSize         = 1000
+)
+
+// Minimal config structs matching the ergo YAML structure.
+// Field names are lowercased by yaml.v2 when no tag is present.
+
+type mysqlConfig struct {
+	Host            string
+	Port            int
+	SocketPath      string `yaml:"socket-path"`
+	User            string
+	Password        string
+	HistoryDatabase string `yaml:"history-database"`
+}
+
+type postgresConfig struct {
+	Host            string
+	Port            int
+	SocketPath      string `yaml:"socket-path"`
+	User            string
+	Password        string
+	HistoryDatabase string `yaml:"history-database"`
+	URI             string `yaml:"uri"`
+	SSLMode         string `yaml:"ssl-mode"`
+}
+
+type ergoConfig struct {
+	Datastore struct {
+		MySQL      mysqlConfig    `yaml:"mysql"`
+		PostgreSQL postgresConfig `yaml:"postgresql"`
+	}
+}
+
+// mysqlDSN builds a go-sql-driver/mysql DSN from config.
+// Copied from irc/mysql/history.go (*MySQL).open().
+func mysqlDSN(c mysqlConfig) string {
+	var address string
+	if c.SocketPath != "" {
+		address = fmt.Sprintf("unix(%s)", c.SocketPath)
+	} else {
+		port := c.Port
+		if port == 0 {
+			port = 3306
+		}
+		address = fmt.Sprintf("tcp(%s:%d)", c.Host, port)
+	}
+	return fmt.Sprintf("%s:%s@%s/%s", c.User, c.Password, address, c.HistoryDatabase)
+}
+
+// postgresURI builds a libpq URI from config.
+// Copied from irc/postgresql/history.go (*Config).buildURI().
+func postgresURI(c postgresConfig) string {
+	if c.URI != "" {
+		return c.URI
+	}
+	u := &url.URL{
+		Scheme: "postgresql",
+		Path:   "/" + c.HistoryDatabase,
+	}
+	q := url.Values{}
+	if c.SocketPath != "" {
+		q.Set("host", c.SocketPath)
+		if c.User != "" || c.Password != "" {
+			u.User = url.UserPassword(c.User, c.Password)
+		}
+	} else {
+		port := c.Port
+		if port == 0 {
+			port = 5432
+		}
+		host := c.Host
+		if host == "" {
+			host = "localhost"
+		}
+		u.Host = fmt.Sprintf("%s:%d", host, port)
+		if c.User != "" || c.Password != "" {
+			u.User = url.UserPassword(c.User, c.Password)
+		}
+	}
+	sslMode := c.SSLMode
+	if sslMode == "" {
+		sslMode = "disable"
+	}
+	q.Set("sslmode", sslMode)
+	u.RawQuery = q.Encode()
+	return u.String()
+}
+
+func main() {
+	configPath := flag.String("config", "ircd.yaml", "path to ergo config file")
+	flag.Parse()
+
+	data, err := os.ReadFile(*configPath)
+	if err != nil {
+		log.Fatalf("read config: %v", err)
+	}
+	var config ergoConfig
+	if err := yaml.Unmarshal(data, &config); err != nil {
+		log.Fatalf("parse config: %v", err)
+	}
+
+	mysqlDB, err := sql.Open("mysql", mysqlDSN(config.Datastore.MySQL))
+	if err != nil {
+		log.Fatalf("open mysql: %v", err)
+	}
+	defer mysqlDB.Close()
+	if err := mysqlDB.Ping(); err != nil {
+		log.Fatalf("ping mysql: %v", err)
+	}
+	log.Println("connected to MySQL")
+
+	pgDB, err := sql.Open("pgx", postgresURI(config.Datastore.PostgreSQL))
+	if err != nil {
+		log.Fatalf("open postgres: %v", err)
+	}
+	defer pgDB.Close()
+	if err := pgDB.Ping(); err != nil {
+		log.Fatalf("ping postgres: %v", err)
+	}
+	log.Println("connected to PostgreSQL")
+
+	log.Println("setting up PostgreSQL schema")
+	if err := setupSchema(pgDB); err != nil {
+		log.Fatalf("setup schema: %v", err)
+	}
+
+	tables := []struct {
+		name string
+		fn   func(*sql.DB, *sql.DB) (int, error)
+	}{
+		{"history", copyHistory},
+		{"sequence", copySequence},
+		{"conversations", copyConversations},
+		{"correspondents", copyCorrespondents},
+		{"account_messages", copyAccountMessages},
+		{"forget", copyForget},
+	}
+	for _, t := range tables {
+		log.Printf("copying %s...", t.name)
+		n, err := t.fn(mysqlDB, pgDB)
+		if err != nil {
+			log.Fatalf("copy %s: %v", t.name, err)
+		}
+		log.Printf("  %d rows", n)
+	}
+
+	log.Println("resetting sequences")
+	if err := resetSequences(pgDB); err != nil {
+		log.Fatalf("reset sequences: %v", err)
+	}
+
+	log.Println("done")
+}
+
+// setupSchema drops and recreates all tables and indexes.
+// Table definitions and indexes are copied from irc/postgresql/history.go.
+func setupSchema(db *sql.DB) error {
+	drops := []string{
+		"DROP TABLE IF EXISTS forget CASCADE",
+		"DROP TABLE IF EXISTS account_messages CASCADE",
+		"DROP TABLE IF EXISTS correspondents CASCADE",
+		"DROP TABLE IF EXISTS conversations CASCADE",
+		"DROP TABLE IF EXISTS sequence CASCADE",
+		"DROP TABLE IF EXISTS history CASCADE",
+		"DROP TABLE IF EXISTS metadata CASCADE",
+	}
+	for _, stmt := range drops {
+		if _, err := db.Exec(stmt); err != nil {
+			return fmt.Errorf("%s: %w", stmt, err)
+		}
+	}
+
+	stmts := []string{
+		`CREATE TABLE metadata (
+			key_name VARCHAR(32) PRIMARY KEY,
+			value VARCHAR(32) NOT NULL
+		)`,
+
+		`CREATE TABLE history (
+			id BIGSERIAL PRIMARY KEY,
+			data BYTEA NOT NULL,
+			msgid BYTEA NOT NULL CHECK (octet_length(msgid) = 16)
+		)`,
+		`CREATE INDEX idx_history_msgid ON history (msgid)`,
+
+		fmt.Sprintf(`CREATE TABLE sequence (
+			history_id BIGINT NOT NULL PRIMARY KEY,
+			target BYTEA NOT NULL CHECK (octet_length(target) <= %d),
+			nanotime BIGINT NOT NULL CHECK (nanotime >= 0)
+		)`, maxTargetLength),
+		`CREATE INDEX idx_sequence_target_nanotime ON sequence (target, nanotime)`,
+
+		fmt.Sprintf(`CREATE TABLE conversations (
+			id BIGSERIAL PRIMARY KEY,
+			target BYTEA NOT NULL CHECK (octet_length(target) <= %d),
+			correspondent BYTEA NOT NULL CHECK (octet_length(correspondent) <= %d),
+			nanotime BIGINT NOT NULL CHECK (nanotime >= 0),
+			history_id BIGINT NOT NULL
+		)`, maxTargetLength, maxTargetLength),
+		`CREATE INDEX idx_conversations_target_correspondent_nanotime ON conversations (target, correspondent, nanotime)`,
+		`CREATE INDEX idx_conversations_history_id ON conversations (history_id)`,
+
+		fmt.Sprintf(`CREATE TABLE correspondents (
+			id BIGSERIAL PRIMARY KEY,
+			target BYTEA NOT NULL CHECK (octet_length(target) <= %d),
+			correspondent BYTEA NOT NULL CHECK (octet_length(correspondent) <= %d),
+			nanotime BIGINT NOT NULL CHECK (nanotime >= 0),
+			UNIQUE (target, correspondent)
+		)`, maxTargetLength, maxTargetLength),
+		`CREATE INDEX idx_correspondents_target_nanotime ON correspondents (target, nanotime)`,
+		`CREATE INDEX idx_correspondents_nanotime ON correspondents (nanotime)`,
+
+		fmt.Sprintf(`CREATE TABLE account_messages (
+			history_id BIGINT NOT NULL PRIMARY KEY,
+			account BYTEA NOT NULL CHECK (octet_length(account) <= %d)
+		)`, maxTargetLength),
+		`CREATE INDEX idx_account_messages_account_history_id ON account_messages (account, history_id)`,
+
+		fmt.Sprintf(`CREATE TABLE forget (
+			id BIGSERIAL PRIMARY KEY,
+			account BYTEA NOT NULL CHECK (octet_length(account) <= %d)
+		)`, maxTargetLength),
+	}
+	for _, stmt := range stmts {
+		if _, err := db.Exec(stmt); err != nil {
+			return fmt.Errorf("exec: %w\nstatement: %s", err, stmt)
+		}
+	}
+
+	_, err := db.Exec(
+		`INSERT INTO metadata (key_name, value) VALUES ($1, $2), ($3, $4)`,
+		"db.version", latestSchema, "db.minorversion", latestMinorSchema,
+	)
+	return err
+}
+
+func copyHistory(src, dst *sql.DB) (int, error) {
+	return copyBatched(src, dst,
+		"SELECT id, data, msgid FROM history WHERE id > ? ORDER BY id LIMIT ?",
+		"INSERT INTO history (id, data, msgid) VALUES ($1, $2, $3)",
+		3,
+	)
+}
+
+func copySequence(src, dst *sql.DB) (int, error) {
+	return copyBatched(src, dst,
+		"SELECT history_id, target, nanotime FROM sequence WHERE history_id > ? ORDER BY history_id LIMIT ?",
+		"INSERT INTO sequence (history_id, target, nanotime) VALUES ($1, $2, $3)",
+		3,
+	)
+}
+
+func copyConversations(src, dst *sql.DB) (int, error) {
+	return copyBatched(src, dst,
+		"SELECT id, target, correspondent, nanotime, history_id FROM conversations WHERE id > ? ORDER BY id LIMIT ?",
+		"INSERT INTO conversations (id, target, correspondent, nanotime, history_id) VALUES ($1, $2, $3, $4, $5)",
+		5,
+	)
+}
+
+func copyCorrespondents(src, dst *sql.DB) (int, error) {
+	return copyBatched(src, dst,
+		"SELECT id, target, correspondent, nanotime FROM correspondents WHERE id > ? ORDER BY id LIMIT ?",
+		"INSERT INTO correspondents (id, target, correspondent, nanotime) VALUES ($1, $2, $3, $4)",
+		4,
+	)
+}
+
+func copyAccountMessages(src, dst *sql.DB) (int, error) {
+	return copyBatched(src, dst,
+		"SELECT history_id, account FROM account_messages WHERE history_id > ? ORDER BY history_id LIMIT ?",
+		"INSERT INTO account_messages (history_id, account) VALUES ($1, $2)",
+		2,
+	)
+}
+
+func copyForget(src, dst *sql.DB) (int, error) {
+	return copyBatched(src, dst,
+		"SELECT id, account FROM forget WHERE id > ? ORDER BY id LIMIT ?",
+		"INSERT INTO forget (id, account) VALUES ($1, $2)",
+		2,
+	)
+}
+
+// copyBatched copies rows from src to dst in batches using keyset pagination on
+// the first (primary key) column. srcQuery must accept (lastID int64, limit int)
+// and return rows ordered by that column. One transaction is committed per batch.
+func copyBatched(src, dst *sql.DB, srcQuery, dstInsert string, ncols int) (int, error) {
+	vals := make([]any, ncols)
+	ptrs := make([]any, ncols)
+	for i := range vals {
+		ptrs[i] = &vals[i]
+	}
+
+	var lastID int64
+	total := 0
+	for {
+		rows, err := src.Query(srcQuery, lastID, batchSize)
+		if err != nil {
+			return total, fmt.Errorf("query: %w", err)
+		}
+
+		tx, err := dst.Begin()
+		if err != nil {
+			rows.Close()
+			return total, fmt.Errorf("begin tx: %w", err)
+		}
+
+		batchCount := 0
+		for rows.Next() {
+			if err := rows.Scan(ptrs...); err != nil {
+				rows.Close()
+				tx.Rollback()
+				return total, fmt.Errorf("scan: %w", err)
+			}
+			// MySQL returns BIGINT UNSIGNED as uint64; convert to int64 for PostgreSQL.
+			for i, v := range vals {
+				if u, ok := v.(uint64); ok {
+					vals[i] = int64(u)
+				}
+			}
+			if _, err := tx.Exec(dstInsert, vals...); err != nil {
+				rows.Close()
+				tx.Rollback()
+				return total, fmt.Errorf("insert: %w", err)
+			}
+			if id, ok := vals[0].(int64); ok {
+				lastID = id
+			}
+			batchCount++
+		}
+		rows.Close()
+		if err := rows.Err(); err != nil {
+			tx.Rollback()
+			return total, fmt.Errorf("rows: %w", err)
+		}
+		if err := tx.Commit(); err != nil {
+			return total, fmt.Errorf("commit: %w", err)
+		}
+		total += batchCount
+		log.Printf("  %d rows copied so far", total)
+		if batchCount < batchSize {
+			break
+		}
+	}
+	return total, nil
+}
+
+func resetSequences(db *sql.DB) error {
+	seqs := []struct{ seq, table, col string }{
+		{"history_id_seq", "history", "id"},
+		{"conversations_id_seq", "conversations", "id"},
+		{"correspondents_id_seq", "correspondents", "id"},
+		{"forget_id_seq", "forget", "id"},
+	}
+	for _, s := range seqs {
+		if _, err := db.Exec(fmt.Sprintf(
+			"SELECT setval('%s', COALESCE((SELECT MAX(%s) FROM %s), 1))",
+			s.seq, s.col, s.table,
+		)); err != nil {
+			return fmt.Errorf("reset %s: %w", s.seq, err)
+		}
+	}
+	return nil
+}