diff --git a/chrome/content/zotero/bindings/zoterosearch.xml b/chrome/content/zotero/bindings/zoterosearch.xml
index dea7fc4f1..365654111 100644
--- a/chrome/content/zotero/bindings/zoterosearch.xml
+++ b/chrome/content/zotero/bindings/zoterosearch.xml
@@ -542,7 +542,9 @@
 							
 							this.mode = condition['mode'];
 							this.id('operatorsmenu').value = condition['operator'];
-							this.value = prefix + condition['value'];
+							this.value = prefix +
+								(condition.value ? condition.value : '');
+
 							this.dontupdate = false;
 						}
 						
diff --git a/chrome/content/zotero/xpcom/search.js b/chrome/content/zotero/xpcom/search.js
index 39f46005a..51e101778 100644
--- a/chrome/content/zotero/xpcom/search.js
+++ b/chrome/content/zotero/xpcom/search.js
@@ -1142,7 +1142,8 @@ Zotero.Search.prototype._buildQuery = function(){
 							case 'isNot': // excluded with NOT IN above
 								// Automatically cast values which might
 								// have been stored as integers
-								if (condition.value.match(/^[1-9]+[0-9]*$/)) {
+								if (condition.value
+										&& condition.value.match(/^[1-9]+[0-9]*$/)) {
 									condSQL += ' LIKE ?';
 								}
 								else {