diff --git a/lib/revalidator.js b/lib/revalidator.js
index 58476b0..d6e26a2 100644
--- a/lib/revalidator.js
+++ b/lib/revalidator.js
@@ -275,7 +275,7 @@
       }
     }
 
-    if (schema.format && options.validateFormats) {
+    if (schema.format && options.validateFormats && typeof value === 'string') {
       format = schema.format;
 
       if (options.validateFormatExtensions) { spec = validate.formatExtensions[format] }