diff --git a/src/php/Core/DB.php b/src/php/Core/DB.php
index 5d90d3e6d..0f10c9185 100644
--- a/src/php/Core/DB.php
+++ b/src/php/Core/DB.php
@@ -98,13 +98,27 @@ public static function table_exists( string $table_name, bool $refresh = false )
 
 	/**
 	 * Create the snippet tables, or upgrade them if they already exist
+	 *
+	 * @return bool Whether every table was created or upgraded.
 	 */
-	public function create_or_upgrade_tables() {
-		if ( is_multisite() ) {
-			$this->create_table( $this->ms_table );
-		}
+	public function create_or_upgrade_tables(): bool {
+		$network_okay = ! is_multisite() || $this->create_table( $this->ms_table );
+		return $this->create_table( $this->table ) && $network_okay;
+	}
+
+	/**
+	 * Upgrade a table that a write has just failed on because it lacks a column.
+	 *
+	 * A table that missed an upgrade fails every save that writes a column it does not have.
+	 *
+	 * @param string $table_name Table the write failed on.
+	 *
+	 * @return bool Whether the table was upgraded, so the write can be retried.
+	 */
+	public static function upgrade_after_unknown_column( string $table_name ): bool {
+		global $wpdb;
 
-		$this->create_table( $this->table );
+		return false !== stripos( (string) $wpdb->last_error, 'Unknown column' ) && self::create_table( $table_name );
 	}
 
 	/**
@@ -322,7 +336,7 @@ private static function fetch_snippets_from_table( string $table_name, array $sc
 			: 'AND active <> -1';
 
 		$snippets = $wpdb->get_results(
-			// phpcs:disable WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
+		// phpcs:disable WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare
 			$wpdb->prepare(
 				"
 				SELECT id, code, scope, active, priority
diff --git a/src/php/Settings/settings.php b/src/php/Settings/settings.php
index 62ebd0a16..a250593d3 100644
--- a/src/php/Settings/settings.php
+++ b/src/php/Settings/settings.php
@@ -217,7 +217,7 @@ function register_plugin_settings() {
 			// accessible name. Checkboxes render their own labels, and
 			// callback/action fields have no single control to point at.
 			$labelable_types = [ 'text', 'number', 'select' ];
-			$field_args      = [];
+			$field_args = [];
 
 			if ( isset( $field['type'] ) && in_array( $field['type'], $labelable_types, true ) ) {
 				$field_args['label_for'] = $field_object->element_id;
@@ -259,7 +259,7 @@ function register_plugin_settings() {
  *
  * @param array<string, mixed>                    $field    Field definition.
  * @param array<string, array<string,mixed>>      $settings Current settings values.
- * @param array<string, array<string,mixed>>|null $input Optional raw input values.
+ * @param array<string, array<string,mixed>>|null $input    Optional raw input values.
  *
  * @return bool
  */
@@ -365,7 +365,7 @@ function process_settings_actions( array $input ): ?array {
 		add_settings_error(
 			OPTION_NAME,
 			'settings_reset',
-			__( 'All settings have been reset to their defaults.', 'code-snippets' ),
+			esc_html__( 'All settings have been reset to their defaults.', 'code-snippets' ),
 			'updated'
 		);
 
@@ -374,14 +374,25 @@ function process_settings_actions( array $input ): ?array {
 	}
 
 	if ( isset( $input['debug']['database_update'] ) ) {
-		code_snippets()->db->create_or_upgrade_tables();
+		if ( code_snippets()->db->create_or_upgrade_tables() ) {
+			add_settings_error(
+				OPTION_NAME,
+				'database_update_done',
+				esc_html__( 'Successfully performed database table upgrade.', 'code-snippets' ),
+				'updated'
+			);
+		} else {
+			global $wpdb;
 
-		add_settings_error(
-			OPTION_NAME,
-			'database_update_done',
-			__( 'Successfully performed database table upgrade.', 'code-snippets' ),
-			'updated'
-		);
+			/* translators: %s: database error message */
+			$error_text = __( 'The database table upgrade did not complete: %s', 'code-snippets' );
+
+			add_settings_error(
+				OPTION_NAME,
+				'database_update_failed',
+				esc_html( sprintf( $error_text, $wpdb->last_error ) ),
+			);
+		}
 	}
 
 	if ( isset( $input['debug']['reset_caches'] ) ) {
@@ -406,29 +417,27 @@ function process_settings_actions( array $input ): ?array {
 		$refresh_failure = Version_Switch::get_refresh_failure();
 
 		if ( $refresh_failure ) {
+			/* translators: %s: reason the plugin versions could not be listed. */
+			$message = __( 'Successfully reset snippets caches, but the available plugin versions could not be listed: %s', 'code-snippets' );
+
 			add_settings_error(
 				OPTION_NAME,
 				'snippet_caches_reset',
-				sprintf(
-					/* translators: %s: reason the plugin versions could not be listed. */
-					__( 'Successfully reset snippets caches, but the available plugin versions could not be listed: %s', 'code-snippets' ),
-					$refresh_failure
-				)
+				esc_html( sprintf( $message, $refresh_failure ) ),
 			);
 		} else {
+			/* translators: %d: number of plugin versions available to install. */
+			$message = _n(
+				'Successfully reset snippets caches. %d plugin version is available to install.',
+				'Successfully reset snippets caches. %d plugin versions are available to install.',
+				count( $available_versions ),
+				'code-snippets'
+			);
+
 			add_settings_error(
 				OPTION_NAME,
 				'snippet_caches_reset',
-				sprintf(
-					/* translators: %d: number of plugin versions available to install. */
-					_n(
-						'Successfully reset snippets caches. %d plugin version is available to install.',
-						'Successfully reset snippets caches. %d plugin versions are available to install.',
-						count( $available_versions ),
-						'code-snippets'
-					),
-					count( $available_versions )
-				),
+				esc_html( sprintf( $message, count( $available_versions ) ) ),
 				'updated'
 			);
 		}
diff --git a/src/php/snippet-ops.php b/src/php/snippet-ops.php
index d43f5f056..6770200de 100644
--- a/src/php/snippet-ops.php
+++ b/src/php/snippet-ops.php
@@ -809,7 +809,14 @@ function save_snippet( $snippet ): ?Snippet {
 	// Create a new snippet if the ID is not set.
 	if ( 0 === $snippet->id ) {
 		$data['created_by'] = $author_id;
-		$result = $wpdb->insert( $table, $data, '%s' );
+		$format = '%s';
+
+		$result = $wpdb->insert( $table, $data, $format );
+
+		if ( false === $result && Core\DB::upgrade_after_unknown_column( $table ) ) {
+			$result = $wpdb->insert( $table, $data, $format );
+		}
+
 		if ( false === $result ) {
 			return null;
 		}
@@ -828,8 +835,20 @@ function save_snippet( $snippet ): ?Snippet {
 		// Otherwise, update the snippet data.
 		$existing = get_snippet( $snippet->id, $snippet->network );
 
+		$where = [ 'id' => $snippet->id ];
+		$where_format = [ '%d' ];
+
+		$result = $wpdb->update( $table, $data, $where, null, $where_format );
+
+		if ( false === $result && Core\DB::upgrade_after_unknown_column( $table ) ) {
+			$result = $wpdb->update( $table, $data, $where, null, $where_format );
+		}
+
+		if ( false === $result ) {
+			return null;
+		}
+
 		set_snippet_locked( $snippet->id, $snippet->locked, $snippet->network );
-		$wpdb->update( $table, $data, [ 'id' => $snippet->id ], null, [ '%d' ] );
 
 		// The row has changed, so the cached list no longer describes it. It is
 		// dropped before the snippet is read back, because everything below —
diff --git a/tests/unit/Core/DB_Test.php b/tests/unit/Core/DB_Test.php
new file mode 100644
index 000000000..7b7a27d98
--- /dev/null
+++ b/tests/unit/Core/DB_Test.php
@@ -0,0 +1,158 @@
+<?php
+
+namespace Code_Snippets\Core;
+
+use Code_Snippets\Model\Snippet;
+use Code_Snippets\UnitTestCase;
+use function Code_Snippets\code_snippets;
+use function Code_Snippets\get_snippet;
+use function Code_Snippets\save_snippet;
+
+// phpcs:disable WordPress.DB.DirectDatabaseQuery, WordPress.DB.PreparedSQL -- tests stand in and inspect the snippets table directly.
+
+/**
+ * Tests for the snippets table and writes to it.
+ */
+class DB_Test extends UnitTestCase {
+
+	/**
+	 * Whether a test replaced the snippets table with one from before the authorship columns.
+	 *
+	 * @var bool
+	 */
+	private bool $shadowed = false;
+
+	/**
+	 * Remove the replacement table.
+	 *
+	 * @return void
+	 */
+	public function tear_down() {
+		global $wpdb;
+
+		if ( $this->shadowed ) {
+			$wpdb->query( 'DROP TEMPORARY TABLE IF EXISTS `' . code_snippets()->db->table . '`' );
+			$this->shadowed = false;
+		}
+
+		remove_all_filters( 'query' );
+		parent::tear_down();
+	}
+
+	/**
+	 * Stand in a snippets table that missed the upgrade adding the authorship columns.
+	 *
+	 * A temporary table hides the real one of the same name for this connection only.
+	 *
+	 * @return void
+	 */
+	private function shadow_table_without_authorship(): void {
+		global $wpdb;
+
+		$table = code_snippets()->db->table;
+
+		$wpdb->query(
+			"CREATE TEMPORARY TABLE `$table` (
+				id BIGINT(20) NOT NULL AUTO_INCREMENT,
+				name TINYTEXT NOT NULL,
+				description TEXT NOT NULL,
+				code LONGTEXT NOT NULL,
+				tags LONGTEXT NOT NULL,
+				scope VARCHAR(15) NOT NULL DEFAULT 'global',
+				condition_id BIGINT(20) NOT NULL DEFAULT 0,
+				priority SMALLINT NOT NULL DEFAULT 10,
+				active TINYINT(1) NOT NULL DEFAULT 0,
+				modified DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+				revision BIGINT(20) NOT NULL DEFAULT 1,
+				cloud_id VARCHAR(255) NULL,
+				PRIMARY KEY (id)
+			)"
+		);
+
+		$this->shadowed = true;
+		DB::table_exists( $table, true );
+	}
+
+	/**
+	 * The names of the columns the current snippets table has.
+	 *
+	 * @return string[]
+	 */
+	private function columns(): array {
+		global $wpdb;
+
+		return $wpdb->get_col( 'SHOW COLUMNS FROM `' . code_snippets()->db->table . '`' );
+	}
+
+	/**
+	 * A table that missed the authorship upgrade is upgraded by the first save, which then succeeds.
+	 *
+	 * @return void
+	 */
+	public function test_saving_upgrades_a_table_missing_a_column(): void {
+		$this->shadow_table_without_authorship();
+		$this->assertNotContains( 'updated_by', $this->columns() );
+
+		$suppressed = $GLOBALS['wpdb']->suppress_errors();
+		$created    = save_snippet(
+			new Snippet(
+				[
+					'name' => 'Created on an old table',
+					'code' => '// one',
+				]
+			)
+		);
+		$GLOBALS['wpdb']->suppress_errors( $suppressed );
+
+		$this->assertNotNull( $created );
+		$this->assertGreaterThan( 0, $created->id );
+		$this->assertContains( 'created_by', $this->columns() );
+		$this->assertContains( 'updated_by', $this->columns() );
+
+		$created->code = '// two';
+		$this->assertNotNull( save_snippet( $created ) );
+		$this->assertSame( '// two', get_snippet( $created->id )->code );
+	}
+
+	/**
+	 * An edit that cannot be written is reported as failed rather than returning the unchanged snippet.
+	 *
+	 * @return void
+	 */
+	public function test_failed_update_returns_null(): void {
+		$snippet = save_snippet(
+			new Snippet(
+				[
+					'name' => 'Cannot be updated',
+					'code' => '// before',
+				]
+			)
+		);
+		$table   = code_snippets()->db->table;
+
+		add_filter(
+			'query',
+			static fn( string $query ): string => 0 === strpos( $query, "UPDATE `$table`" ) ? 'UPDATE `cs_missing_table` SET id = 1' : $query
+		);
+
+		$snippet->code = '// after';
+
+		$suppressed = $GLOBALS['wpdb']->suppress_errors();
+		$saved      = save_snippet( $snippet );
+		$GLOBALS['wpdb']->suppress_errors( $suppressed );
+
+		$this->assertNull( $saved );
+
+		remove_all_filters( 'query' );
+		$this->assertSame( '// before', get_snippet( $snippet->id )->code );
+	}
+
+	/**
+	 * Upgrading the tables reports success when they match the current schema.
+	 *
+	 * @return void
+	 */
+	public function test_create_or_upgrade_tables_reports_success(): void {
+		$this->assertTrue( code_snippets()->db->create_or_upgrade_tables() );
+	}
+}