diff --git a/index.js b/index.js
index 936c9dd..80fc3c8 100644
--- a/index.js
+++ b/index.js
@@ -342,7 +342,7 @@ function setDefaults(defs) {
       }
     }
 
-    if (opts.body || opts.json || opts.form || opts.formData) {
+    if (opts.body || 'string' === typeof opts.json || opts.form || opts.formData) {
       reqOpts.method = (reqOpts.method || 'POST').toUpperCase();
     } else {
       reqOpts.method = (reqOpts.method || 'GET').toUpperCase();