diff --git a/CHANGELOG.md b/CHANGELOG.md
index e2611bb..f1b9275 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ IMPORTANT NOTE: This version only works on CACTI 1.x++!
 
 --- develop ---
 
+* issue#277: Allow map duplication when the debug column is absent while preserving its default when present
 * issue#151: Keep standalone editor controls visible and use theme-aware dialog contrast
 * issue#275: Load permitted editor picker results in bounded pages, search interface descriptions, and encode graph search terms
 * issue#274: Fit hover popups to their graph content and close them immediately when leaving map links, preserving graph proportions and meaningful captions
diff --git a/tests/Support/MapDuplicatePayload.php b/tests/Support/MapDuplicatePayload.php
new file mode 100644
index 0000000..ad558dd
--- /dev/null
+++ b/tests/Support/MapDuplicatePayload.php
@@ -0,0 +1,96 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2022-2026 The Cacti Group, Howard Jones                    |
+ | Licensed under the GNU General Public License, version 2.              |
+ +-------------------------------------------------------------------------+
+*/
+
+// Run the actual function without executing the management page dispatcher.
+$source = file_get_contents(__DIR__ . '/../../weathermap-cacti-plugin-mgmt.php');
+$start  = strpos($source, 'function map_duplicate(');
+$end    = strpos($source, "\n/**", $start);
+
+if ($start === false || $end === false) {
+	throw new RuntimeException('Unable to locate the map duplication function.');
+}
+eval(substr($source, $start, $end - $start));
+
+/**
+ * Return the source map fixture.
+ *
+ * @param string $sql    Query.
+ * @param array  $params Query parameters.
+ *
+ * @return array Source map row.
+ */
+function db_fetch_row_prepared($sql, $params) {
+	return ['group_id' => 2, 'active' => 1, 'configfile' => 'Original.conf', 'titlecache' => 'Original Map',
+		'thumb_height'    => 150, 'thumb_width' => 200, 'schedule' => '* * * * *', 'archiving' => 0];
+}
+
+/**
+ * Return the existing maximum map sort order.
+ *
+ * @param string $sql Query.
+ *
+ * @return int Maximum sort order.
+ */
+function db_fetch_cell($sql) {
+	return 9;
+}
+
+/**
+ * Count a fixture array.
+ *
+ * @param array $value Array to count.
+ *
+ * @return int Array size.
+ */
+function cacti_sizeof($value) {
+	return count($value);
+}
+
+/**
+ * Supply a destination filename without touching the filesystem.
+ *
+ * @param string $file Source filename.
+ *
+ * @return string Destination filename.
+ */
+function map_get_next_name($file) {
+	return 'Original_copy.conf';
+}
+
+/**
+ * Report the selected schema shape.
+ *
+ * @param string $table  Table name.
+ * @param string $column Column name.
+ *
+ * @return bool Whether the debug column exists.
+ */
+function db_column_exists($table, $column) {
+	if ($table !== 'weathermap_maps' || $column !== 'debug') {
+		throw new RuntimeException('Unexpected column lookup.');
+	}
+
+	return $GLOBALS['argv'][1] === 'present';
+}
+
+/**
+ * Capture the actual save payload and stop before file copying/polling.
+ *
+ * @param array  $payload Map fields to save.
+ * @param string $table   Destination table.
+ *
+ * @return int Zero prevents further side effects in the fixture.
+ */
+function sql_save($payload, $table) {
+	$GLOBALS['duplicate_save'] = ['table' => $table, 'payload' => $payload];
+
+	return 0;
+}
+
+map_duplicate(5, '<map_title> Copy');
+print json_encode($GLOBALS['duplicate_save'], JSON_THROW_ON_ERROR);
diff --git a/tests/Unit/MapDuplicateSchemaTest.php b/tests/Unit/MapDuplicateSchemaTest.php
new file mode 100644
index 0000000..50ca414
--- /dev/null
+++ b/tests/Unit/MapDuplicateSchemaTest.php
@@ -0,0 +1,31 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2022-2026 The Cacti Group, Howard Jones                    |
+ | Licensed under the GNU General Public License, version 2.              |
+ +-------------------------------------------------------------------------+
+*/
+
+it('SavesTheDuplicatePayloadForBothDebugSchemaShapes', function (bool $has_debug): void {
+	$command = escapeshellarg(PHP_BINARY) . ' ' . escapeshellarg(dirname(__DIR__) . '/Support/MapDuplicatePayload.php') . ' ' . ($has_debug ? 'present' : 'absent');
+	$lines   = [];
+	exec($command, $lines, $status);
+	expect($status)->toBe(0);
+	$saved = json_decode(implode("\n", $lines), true, 512, JSON_THROW_ON_ERROR);
+	expect($saved['table'])->toBe('weathermap_maps');
+	$payload = $saved['payload'];
+	expect(array_key_exists('debug', $payload))->toBe($has_debug);
+
+	if ($has_debug) {
+		expect($payload['debug'])->toBe('off');
+	}
+	expect($payload['id'])->toBe(0)
+		->and($payload['sortorder'])->toBe(10)
+		->and($payload['titlecache'])->toBe('Original Map Copy')
+		->and($payload['configfile'])->toBe('Original_copy.conf')
+		->and($payload['group_id'])->toBe(2)
+		->and($payload['active'])->toBe(1)
+		->and($payload['imagefile'])->toBe('')
+		->and($payload['htmlfile'])->toBe('')
+		->and($payload['warncount'])->toBe(0);
+})->with([false, true]);
diff --git a/weathermap-cacti-plugin-mgmt.php b/weathermap-cacti-plugin-mgmt.php
index 896bc90..87e7baf 100644
--- a/weathermap-cacti-plugin-mgmt.php
+++ b/weathermap-cacti-plugin-mgmt.php
@@ -1936,7 +1936,9 @@ function map_duplicate($id, $titlecache, $configfile = null) {
 		$save['htmlfile']     = '';
 		$save['filehash']     = '';
 		$save['warncount']    = 0;
-		$save['debug']        = 'off';
+		if (db_column_exists('weathermap_maps', 'debug')) {
+			$save['debug'] = 'off';
+		}
 		$save['config']       = '';
 		$save['thumb_height'] = $map['thumb_height'];
 		$save['thumb_width']  = $map['thumb_width'];