diff --git a/js/jquery.tablesorter.js b/js/jquery.tablesorter.js
index 9f851441..b3a13955 100644
--- a/js/jquery.tablesorter.js
+++ b/js/jquery.tablesorter.js
@@ -1243,6 +1243,8 @@
 			};
 
 			// Natural sort - https://github.com/overset/javascript-natural-sort (date sorting removed)
+			// this function will only accept strings, or you'll see "TypeError: undefined is not a function"
+			// I could add a = a.toString(); b = b.toString(); but it'll slow down the sort overall
 			ts.sortNatural = function(a, b) {
 				if (a === b) { return 0; }
 				var xN, xD, yN, yD, xF, yF, i, mx,
diff --git a/js/jquery.tablesorter.widgets.js b/js/jquery.tablesorter.widgets.js
index dcddf060..32711f73 100644
--- a/js/jquery.tablesorter.widgets.js
+++ b/js/jquery.tablesorter.widgets.js
@@ -1082,7 +1082,8 @@ ts.filter = {
 			// sort parsed select options
 			cts = c.textSorter || '';
 			parsed.sort(function(a, b){
-				var x = a.p, y = b.p;
+				// sortNatural breaks if you don't pass it strings
+				var x = a.p.toString(), y = b.p.toString();
 				if ($.isFunction(cts)) {
 					// custom OVERALL text sorter
 					return cts(x, y, true, column, table);