diff --git a/lib/index.js b/lib/index.js
index ac3f41b..a34fbe2 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -15,6 +15,10 @@ const ONEMB = bytes('1mb');
 // how many concurrent HTTP/2 stream uploads
 const MAX_CONCURRENT = 10;
 
+// check if running windows
+const IS_WIN = /^win/.test(process.platform);
+const SEP = IS_WIN ? '\\' : '/';
+
 export default class Now extends EventEmitter {
   constructor (token, { forceNew = false, debug = false }) {
     super();
@@ -194,9 +198,9 @@ export default class Now extends EventEmitter {
 }
 
 function toRelative (path, base) {
-  const fullBase = /\/$/.test(base) ? base + '/' : base;
+  const fullBase = base.endsWith(SEP) ? base + SEP : base;
   const relative = path.substr(fullBase.length);
-  if (relative.startsWith('/')) return relative.substr(1);
+  if (relative.startsWith(SEP)) return relative.substr(1);
   return relative;
 }