diff --git a/controllers/TagsController.php b/controllers/TagsController.php
index dad6a482..abb1a7c3 100644
--- a/controllers/TagsController.php
+++ b/controllers/TagsController.php
@@ -186,6 +186,10 @@ public function tags() {
 				// Filter for specific tags with "?tag=foo || bar"
 				$tagNames = !empty($this->queryParams['tag'])
 					? explode(' || ', $this->queryParams['tag']): array();
+				// Replace \|| with || to allow for tags with literal '||'.
+				$tagNames = array_map(function ($name) {
+					return str_replace("\||", "||", $name);
+				}, $tagNames);
 				Zotero_DB::beginTransaction();
 				foreach ($tagNames as $tagName) {
 					$tagIDs = Zotero_Tags::getIDs($this->objectLibraryID, $tagName);
diff --git a/model/API.inc.php b/model/API.inc.php
index 863104a3..da398538 100644
--- a/model/API.inc.php
+++ b/model/API.inc.php
@@ -1332,6 +1332,11 @@ public static function getSearchParamValues($params, $param) {
 			// Separate into boolean OR parts
 			$parts = preg_split("/\s+\|\|\s+/", $val);
 			
+			// Replace \|| with || to allow for tags with literal '||'.
+			$parts = array_map(function ($part) {
+				return str_replace("\||", "||", $part);
+			}, $parts);
+
 			$val = array(
 				'negation' => $negation,
 				'values' => $parts