diff --git a/lib/path.js b/lib/path.js
index 5d69d2270fe..5fb6656dc4b 100644
--- a/lib/path.js
+++ b/lib/path.js
@@ -177,6 +177,9 @@ if (isWindows) {
       tail += '\\';
     }
 
+    // Convert slashes to backslashes when `device` points to an UNC root.
+    device = device.replace(/\//g, '\\');
+
     return device + (isAbsolute ? '\\' : '') + tail;
   };