diff --git a/src/Pagerfanta/ExtendedPdoAdapter.php b/src/Pagerfanta/ExtendedPdoAdapter.php
index 5f70fe3..34e6a1c 100644
--- a/src/Pagerfanta/ExtendedPdoAdapter.php
+++ b/src/Pagerfanta/ExtendedPdoAdapter.php
@@ -108,6 +108,9 @@ public function getLimitClause($offset, $length)
      */
     public function rewriteCountQuery($query)
     {
+        if (\is_int(\strpos(\strtolower($query), 'union'))) {
+            return '';
+        }
         if (\preg_match('/^\s*SELECT\s+\bDISTINCT\b/is', $query) || \preg_match('/\s+GROUP\s+BY\s+/is', $query)) {
             return '';
         }
diff --git a/tests/Pagerfanta/ExtendedPdoAdapterTest.php b/tests/Pagerfanta/ExtendedPdoAdapterTest.php
index 7c75411..c194bcf 100644
--- a/tests/Pagerfanta/ExtendedPdoAdapterTest.php
+++ b/tests/Pagerfanta/ExtendedPdoAdapterTest.php
@@ -62,6 +62,7 @@ public function splProvider()
             ['SELECT * FROM posts', [], 'SELECT COUNT(*) FROM posts', 50],
             ['SELECT DISTINCT id FROM posts', [], '', 50],
             ['SELECT * FROM posts WHERE id > :num', ['num' => 10], 'SELECT COUNT(*) FROM posts WHERE id > :num', 40],
+            ['SELECT id FROM posts UNION SELECT id FROM posts', [], '', 50],
         ];
     }