diff --git a/src/Tasks/FixBlogDuplicatesTask.php b/src/Tasks/FixBlogDuplicatesTask.php
new file mode 100644
index 0000000..45b905b
--- /dev/null
+++ b/src/Tasks/FixBlogDuplicatesTask.php
@@ -0,0 +1,139 @@
+<?php
+
+namespace SilverStripe\Blog\Tasks;
+
+use SilverStripe\Blog\Model\BlogCategory;
+use SilverStripe\Blog\Model\BlogTag;
+use SilverStripe\Control\Director;
+use SilverStripe\Core\Convert;
+use SilverStripe\Dev\BuildTask;
+use SilverStripe\ORM\DataObject;
+use SilverStripe\ORM\DB;
+use SilverStripe\ORM\Queries\SQLSelect;
+use SilverStripe\View\HTML;
+
+class FixBlogDuplicatesTask extends BuildTask
+{
+    private static $segment = 'FixBlogDuplicatesTask';
+
+    protected $title = 'Fix blog duplicate categories / tags';
+
+    protected $description = 'Merge categories and tags with the same title';
+
+    public function run($request)
+    {
+        $this->dedupe(BlogTag::class, 'BlogPost_Tags', 'BlogTagID');
+        $this->dedupe(BlogCategory::class, 'BlogPost_Categories', 'BlogCategoryID');
+    }
+
+    /**
+     * Log message to console / page
+     *
+     * @param string $message
+     */
+    protected function message($message)
+    {
+        if (Director::is_cli()) {
+            echo "{$message}\n";
+        } else {
+            echo HTML::createTag('p', [], Convert::raw2xml($message));
+        }
+    }
+
+    /**
+     * Progress used for CLI output
+     *
+     * @var int
+     */
+    protected $printedDots = 0;
+
+    /**
+     * Render progress dots (20 dots per column)
+     *
+     * @param        $current
+     * @param int    $total
+     * @param string $character
+     */
+    protected function progress($current, $total = 0, $character = '.')
+    {
+        if (!Director::is_cli()) {
+            return;
+        }
+        while ($this->printedDots < $current) {
+            echo $character;
+            $this->printedDots++;
+            if ($this->printedDots % 80 === 0) {
+                if ($total) {
+                    $len = strlen($total);
+                    echo str_pad("{$this->printedDots}/{$total}", $len * 2 + 2, ' ', STR_PAD_LEFT);
+                }
+                echo "\n";
+            }
+        }
+    }
+
+    /**
+     * Deduplicate the given class
+     *
+     * @param string $class         Class name to dedupe
+     * @param string $mappingTable  Table name mapping
+     * @param string $relationField Name of foreign key relation field on mapping table
+     */
+    protected function dedupe($class, $mappingTable, $relationField)
+    {
+        $this->printedDots = 0;
+
+        // Find all duplicates
+        $itemTable = DataObject::getSchema()->tableName($class);
+        $duplicates = SQLSelect::create()
+            ->setSelect([
+                'Title' => '"Title"',
+                'Count' => 'COUNT(*)',
+                'UseID' => 'MIN("ID")',
+            ])
+            ->setFrom($itemTable)
+            ->setGroupBy('"Title"')
+            ->setHaving('"Count" > 1');
+
+        $count = $duplicates->count();
+
+        $this->message("Found {$count} items with duplicates for type {$class}");
+
+        if (!$count) {
+            return;
+        }
+
+        $done = 0;
+        foreach ($duplicates->execute() as $duplicate) {
+            $title = $duplicate['Title'];
+            $id = $duplicate['UseID'];
+
+            DB::prepared_query(<<<SQL
+UPDATE "{$mappingTable}"
+INNER JOIN "{$itemTable}" ON "{$mappingTable}"."{$relationField}" = "{$itemTable}"."ID"
+SET "{$mappingTable}"."{$relationField}" = ? 
+WHERE "{$itemTable}"."Title" = ? 
+SQL
+                ,
+                [$id, $title]
+            );
+
+            // Delete duplicates
+            $duplicateItems = DataObject::get($class)->filter([
+                'Title'  => $title,
+                'ID:not' => $id,
+            ]);
+            /** @var DataObject $duplicateItem */
+            foreach ($duplicateItems as $duplicateItem) {
+                $duplicateItem->delete();
+            }
+
+            // Update progress bar
+            $done++;
+            $this->progress($done, $count);
+        }
+
+        $this->progress("");
+        $this->progress("Completed cleaning duplicates for {$class}");
+    }
+}