diff --git a/core/modules/filters/json-ops.js b/core/modules/filters/json-ops.js
index 75a34e94a..0c58964eb 100644
--- a/core/modules/filters/json-ops.js
+++ b/core/modules/filters/json-ops.js
@@ -273,7 +273,10 @@ function setDataItem(data,indexes,value) {
 		lastIndex = $tw.utils.parseInt(lastIndex);
 		if(lastIndex < 0) { lastIndex = lastIndex + current.length };
 	}
-	current[lastIndex] = value;
+	// Only set indexes on objects and arrays
+	if(typeof current === "object") {
+		current[lastIndex] = value;
+	}
 	return data;
 }
 
diff --git a/editions/test/tiddlers/tests/test-json-filters.js b/editions/test/tiddlers/tests/test-json-filters.js
index a8903970a..bfb8a4504 100644
--- a/editions/test/tiddlers/tests/test-json-filters.js
+++ b/editions/test/tiddlers/tests/test-json-filters.js
@@ -124,6 +124,7 @@ describe("json filter tests", function() {
 	});
 
 	it("should support the jsonset operator", function() {
+		expect(wiki.filterTiddlers("[jsonset[a],[aa]]")).toEqual(['"First"','"Second"','"Third"']);
 		expect(wiki.filterTiddlers("[{First}jsonset[]]")).toEqual(['{"a":"one","b":"","c":1.618,"d":{"e":"four","f":["five","six",true,false,null]}}']);
 		expect(wiki.filterTiddlers("[{First}jsonset[],[Antelope]]")).toEqual(['"Antelope"']);
 		expect(wiki.filterTiddlers("[{First}jsonset:number[],[not a number]]")).toEqual(['0']);