diff --git a/bucket/mdbook.json b/bucket/mdbook.json
index 8c12728ae0..4984f70414 100644
--- a/bucket/mdbook.json
+++ b/bucket/mdbook.json
@@ -1,12 +1,12 @@
 {
-    "version": "0.4.37",
+    "version": "0.4.40",
     "description": "Create a book from markdown files.",
     "homepage": "https://github.com/rust-lang/mdBook",
     "license": "MPL-2.0",
     "architecture": {
         "64bit": {
-            "url": "https://github.com/rust-lang/mdBook/releases/download/v0.4.37/mdbook-v0.4.37-x86_64-pc-windows-msvc.zip",
-            "hash": "99a61a99a2529188854c1a2719b1849d92cce0509e6241d11b408fda9e5ba2d9"
+            "url": "https://github.com/rust-lang/mdBook/releases/download/v0.4.40/mdbook-v0.4.40-x86_64-pc-windows-msvc.zip",
+            "hash": "1470e5b06614cb2851e8b3c908dfdef2982b90e6cc6045662512ce66d6c7c5d9"
         }
     },
     "bin": "mdbook.exe",