diff --git a/src/auth/auth.go b/src/auth/auth.go
index 5a11ade..6806c83 100644
--- a/src/auth/auth.go
+++ b/src/auth/auth.go
@@ -2,15 +2,18 @@ package auth
 
 import (
 	"bytes"
+	"context"
 	"crypto/rand"
 	"crypto/sha256"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io"
 	"strconv"
 	"strings"
 
 	"git.handmade.network/hmn/hmn/src/oops"
+	"github.com/jackc/pgx/v4/pgxpool"
 	"golang.org/x/crypto/argon2"
 	"golang.org/x/crypto/pbkdf2"
 )
@@ -54,6 +57,10 @@ func (p HashedPassword) String() string {
 	return fmt.Sprintf("%s$%s$%s$%s", p.Algorithm, p.AlgoConfig, p.Salt, p.Hash)
 }
 
+func (p HashedPassword) IsOutdated() bool {
+	return p.Algorithm != Argon2id
+}
+
 type Argon2idConfig struct {
 	Time      uint32
 	Memory    uint32
@@ -152,7 +159,7 @@ func HashPassword(password string) (HashedPassword, error) {
 
 	cfg := Argon2idConfig{
 		Time:      1,
-		Memory:    40 * 1024 * 1024,
+		Memory:    40 * 1024, // this is in KiB for some reason
 		Threads:   1,
 		KeyLength: keyLength,
 	}
@@ -167,3 +174,16 @@ func HashPassword(password string) (HashedPassword, error) {
 		Hash:       keyEnc,
 	}, nil
 }
+
+var ErrUserDoesNotExist = errors.New("user does not exist")
+
+func UpdatePassword(ctx context.Context, conn *pgxpool.Pool, username string, hp HashedPassword) error {
+	tag, err := conn.Exec(ctx, "UPDATE auth_user SET password = $1 WHERE username = $2", hp.String(), username)
+	if err != nil {
+		return oops.New(err, "failed to update password")
+	} else if tag.RowsAffected() < 1 {
+		return ErrUserDoesNotExist
+	}
+
+	return nil
+}
diff --git a/src/migration/migration.go b/src/migration/migration.go
index 4eb0bfd..60e9a0b 100644
--- a/src/migration/migration.go
+++ b/src/migration/migration.go
@@ -49,7 +49,8 @@ func init() {
 		Short: "Create a new database migration file",
 		Run: func(cmd *cobra.Command, args []string) {
 			if len(args) < 2 {
-				fmt.Println("You must provide a name and a description.")
+				fmt.Printf("You must provide a name and a description.\n\n")
+				cmd.Usage()
 				os.Exit(1)
 			}
 
diff --git a/src/migration/migrations/2021-03-28T152630Z_AllowLongerPasswordHashes.go b/src/migration/migrations/2021-03-28T152630Z_AllowLongerPasswordHashes.go
new file mode 100644
index 0000000..2b22819
--- /dev/null
+++ b/src/migration/migrations/2021-03-28T152630Z_AllowLongerPasswordHashes.go
@@ -0,0 +1,43 @@
+package migrations
+
+import (
+	"context"
+	"time"
+
+	"git.handmade.network/hmn/hmn/src/migration/types"
+	"github.com/jackc/pgx/v4"
+)
+
+func init() {
+	registerMigration(AllowLongerPasswordHashes{})
+}
+
+type AllowLongerPasswordHashes struct{}
+
+func (m AllowLongerPasswordHashes) Version() types.MigrationVersion {
+	return types.MigrationVersion(time.Date(2021, 3, 28, 15, 26, 30, 0, time.UTC))
+}
+
+func (m AllowLongerPasswordHashes) Name() string {
+	return "AllowLongerPasswordHashes"
+}
+
+func (m AllowLongerPasswordHashes) Description() string {
+	return "Increase the storage size limit on hashed passwords"
+}
+
+func (m AllowLongerPasswordHashes) Up(tx pgx.Tx) error {
+	_, err := tx.Exec(context.Background(), `
+		ALTER TABLE auth_user
+			ALTER COLUMN password TYPE VARCHAR(256)
+	`)
+	return err
+}
+
+func (m AllowLongerPasswordHashes) Down(tx pgx.Tx) error {
+	_, err := tx.Exec(context.Background(), `
+		ALTER TABLE auth_user
+			ALTER COLUMN password TYPE VARCHAR(128)
+	`)
+	return err
+}
diff --git a/src/website/routes.go b/src/website/routes.go
index be500ca..abba5ca 100644
--- a/src/website/routes.go
+++ b/src/website/routes.go
@@ -183,6 +183,20 @@ func (s *websiteRoutes) Login(c *RequestContext, p httprouter.Params) {
 	}
 
 	if passwordsMatch {
+		// re-hash and save the user's password if necessary
+		if hashed.IsOutdated() {
+			newHashed, err := auth.HashPassword(password)
+			if err == nil {
+				err := auth.UpdatePassword(c.Context(), s.conn, username, newHashed)
+				if err != nil {
+					c.Logger.Error().Err(err).Msg("failed to update user's password")
+				}
+			} else {
+				c.Logger.Error().Err(err).Msg("failed to re-hash password")
+			}
+			// If errors happen here, we can still continue with logging them in
+		}
+
 		session, err := auth.CreateSession(c.Context(), s.conn, username)
 		if err != nil {
 			c.Errored(http.StatusInternalServerError, oops.New(err, "failed to create session"))