diff --git a/src/html/template/js.go b/src/html/template/js.go
index 239395f8d3..e02fdb9751 100644
--- a/src/html/template/js.go
+++ b/src/html/template/js.go
@@ -123,6 +123,14 @@ var jsonMarshalType = reflect.TypeOf((*json.Marshaler)(nil)).Elem()
 // indirectToJSONMarshaler returns the value, after dereferencing as many times
 // as necessary to reach the base type (or nil) or an implementation of json.Marshal.
 func indirectToJSONMarshaler(a interface{}) interface{} {
+	// text/template now supports passing untyped nil as a func call
+	// argument, so we must support it. Otherwise we'd panic below, as one
+	// cannot call the Type or Interface methods on an invalid
+	// reflect.Value. See golang.org/issue/18716.
+	if a == nil {
+		return nil
+	}
+
 	v := reflect.ValueOf(a)
 	for !v.Type().Implements(jsonMarshalType) && v.Kind() == reflect.Ptr && !v.IsNil() {
 		v = v.Elem()
diff --git a/src/html/template/js_test.go b/src/html/template/js_test.go
index 7484f60b54..cf2a0d2987 100644
--- a/src/html/template/js_test.go
+++ b/src/html/template/js_test.go
@@ -149,6 +149,7 @@ func TestJSValEscaper(t *testing.T) {
 		{"]]>", `"]]\u003e"`},
 		{"</script", `"\u003c/script"`},
 		{"\U0001D11E", "\"\U0001D11E\""}, // or "\uD834\uDD1E"
+		{nil, " null "},
 	}
 
 	for _, test := range tests {