diff --git a/lib/forms.js b/lib/forms.js
index 558e5c8..c4d514d 100644
--- a/lib/forms.js
+++ b/lib/forms.js
@@ -58,7 +58,9 @@ exports.create = function (fields, opts) {
             b.isValid = function () {
                 var form = this;
                 return Object.keys(form.fields).every(function (k) {
-                    return form.fields[k].error === null || typeof form.fields[k].error === 'undefined';
+					var field = form.fields[k];
+					if (is.fn(field.isValid)) { return field.isValid(); }
+                    return field.error === null || typeof field.error === 'undefined';
                 });
             };
             return b;