diff --git a/servo/Cargo.lock b/servo/Cargo.lock
index 9dcd150f5705..bb1d7f6d4f26 100644
--- a/servo/Cargo.lock
+++ b/servo/Cargo.lock
@@ -5,7 +5,7 @@ dependencies = [
  "ipc-channel 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "msg 0.0.1",
  "rust-webvr 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -63,7 +63,7 @@ dependencies = [
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -154,7 +154,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -225,7 +225,7 @@ version = "0.0.1"
 dependencies = [
  "ipc-channel 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_config 0.0.1",
 ]
@@ -301,7 +301,7 @@ dependencies = [
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "ipc-channel 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_traits 0.35.0 (git+https://github.com/servo/webrender)",
 ]
@@ -453,7 +453,7 @@ dependencies = [
  "offscreen_gl_context 0.8.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "profile_traits 0.0.1",
  "script_traits 0.0.1",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_config 0.0.1",
  "servo_rand 0.0.1",
@@ -496,7 +496,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "core-foundation 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -520,7 +520,7 @@ dependencies = [
  "phf 0.7.21 (registry+https://github.com/rust-lang/crates.io-index)",
  "procedural-masquerade 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "quote 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "syn 0.11.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -615,7 +615,7 @@ dependencies = [
  "ipc-channel 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "msg 0.0.1",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 0.9.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -632,7 +632,7 @@ dependencies = [
  "hyper_serde 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "ipc-channel 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "msg 0.0.1",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_url 0.0.1",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -676,7 +676,7 @@ dependencies = [
  "kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -841,7 +841,7 @@ dependencies = [
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -980,7 +980,7 @@ dependencies = [
  "net_traits 0.0.1",
  "ordered-float 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "range 0.0.1",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo-fontconfig 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_atoms 0.0.1",
@@ -1013,7 +1013,7 @@ dependencies = [
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "range 0.0.1",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1205,7 +1205,7 @@ dependencies = [
  "cookie 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "hyper 0.10.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "mime 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1283,7 +1283,7 @@ dependencies = [
  "libc 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
  "mio 0.6.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "uuid 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1379,7 +1379,7 @@ dependencies = [
  "script_layout_interface 0.0.1",
  "script_traits 0.0.1",
  "selectors 0.18.0",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 0.9.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_config 0.0.1",
@@ -1669,7 +1669,7 @@ dependencies = [
  "cssparser 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_traits 0.35.0 (git+https://github.com/servo/webrender)",
 ]
@@ -1703,7 +1703,7 @@ dependencies = [
  "openssl 0.9.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "parse-hosts 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "profile_traits 0.0.1",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 0.9.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo-websocket 0.19.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1768,7 +1768,7 @@ dependencies = [
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "msg 0.0.1",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_config 0.0.1",
  "servo_url 0.0.1",
@@ -1869,7 +1869,7 @@ dependencies = [
  "libloading 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "osmesa-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "user32-sys 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "x11 2.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2064,7 +2064,7 @@ dependencies = [
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "profile_traits 0.0.1",
  "regex 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 0.9.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_config 0.0.1",
@@ -2089,7 +2089,7 @@ dependencies = [
  "energymon 0.3.0 (git+https://github.com/energymon/energymon-rust.git)",
  "ipc-channel 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_config 0.0.1",
  "signpost 0.1.0 (git+https://github.com/pcwalton/signpost.git)",
@@ -2136,7 +2136,7 @@ dependencies = [
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2191,7 +2191,7 @@ dependencies = [
  "gl_generator 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "libloading 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -2286,7 +2286,7 @@ dependencies = [
  "script_plugins 0.0.1",
  "script_traits 0.0.1",
  "selectors 0.18.0",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 0.9.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_atoms 0.0.1",
  "servo_config 0.0.1",
@@ -2370,7 +2370,7 @@ dependencies = [
  "offscreen_gl_context 0.8.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "profile_traits 0.0.1",
  "rustc-serialize 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_url 0.0.1",
  "style_traits 0.0.1",
@@ -2399,7 +2399,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "serde"
-version = "0.9.11"
+version = "0.9.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -2428,7 +2428,7 @@ dependencies = [
  "dtoa 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "itoa 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -2573,7 +2573,7 @@ dependencies = [
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_geometry 0.0.1",
  "servo_url 0.0.1",
@@ -2627,7 +2627,7 @@ version = "0.0.1"
 dependencies = [
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_rand 0.0.1",
  "url 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2698,7 +2698,7 @@ dependencies = [
  "lazy_static 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "phf_shared 0.7.21 (registry+https://github.com/rust-lang/crates.io-index)",
  "precomputed-hash 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "string_cache_codegen 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "string_cache_shared 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -2757,7 +2757,7 @@ dependencies = [
  "rayon 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "selectors 0.18.0",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_atoms 0.0.1",
  "servo_config 0.0.1",
@@ -2797,7 +2797,7 @@ dependencies = [
  "euclid 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_derive 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -3073,7 +3073,7 @@ name = "url_serde"
 version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -3105,7 +3105,7 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "rand 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -3208,7 +3208,7 @@ dependencies = [
  "heapsize 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "ipc-channel 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "offscreen_gl_context 0.8.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -3501,7 +3501,7 @@ dependencies = [
 "checksum same-file 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "d931a44fdaa43b8637009e7632a02adc4f2b2e0733c08caa4cf00e8da4a117a7"
 "checksum scoped_threadpool 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)" = "3ef399c8893e8cb7aa9696e895427fab3a6bf265977bb96e126f24ddd2cda85a"
 "checksum semver 0.1.20 (registry+https://github.com/rust-lang/crates.io-index)" = "d4f410fedcf71af0345d7607d246e7ad15faaadd49d240ee3b24e5dc21a820ac"
-"checksum serde 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)" = "a702319c807c016e51f672e5c77d6f0b46afddd744b5e437d6b8436b888b458f"
+"checksum serde 0.9.15 (registry+https://github.com/rust-lang/crates.io-index)" = "34b623917345a631dc9608d5194cc206b3fe6c3554cd1c75b937e55e285254af"
 "checksum serde_codegen_internals 0.14.1 (registry+https://github.com/rust-lang/crates.io-index)" = "4d52006899f910528a10631e5b727973fe668f3228109d1707ccf5bad5490b6e"
 "checksum serde_derive 0.9.11 (registry+https://github.com/rust-lang/crates.io-index)" = "f15ea24bd037b2d64646b4d934fa99c649be66e3f7b29fb595a5543b212b1452"
 "checksum serde_json 0.9.9 (registry+https://github.com/rust-lang/crates.io-index)" = "dbc45439552eb8fb86907a2c41c1fd0ef97458efb87ff7f878db466eb581824e"
diff --git a/servo/python/servo/devenv_commands.py b/servo/python/servo/devenv_commands.py
index a3e14bee6525..d414a3324bc0 100644
--- a/servo/python/servo/devenv_commands.py
+++ b/servo/python/servo/devenv_commands.py
@@ -11,6 +11,8 @@ from __future__ import print_function, unicode_literals
 from os import path, getcwd, listdir
 
 import sys
+import urllib2
+import json
 
 from mach.decorators import (
     CommandArgument,
@@ -223,6 +225,22 @@ class MachCommands(CommandBase):
             ["git"] + ["grep"] + params + ['--'] + grep_paths + [':(exclude)*.min.js', ':(exclude)*.min.css'],
             env=self.build_env())
 
+    @Command('rustup',
+             description='Update the Rust version to latest master',
+             category='devenv')
+    def rustup(self):
+        url = "https://api.github.com/repos/rust-lang/rust/git/refs/heads/master"
+        commit = json.load(urllib2.urlopen(url))["object"]["sha"]
+        filename = path.join(self.context.topdir, "rust-commit-hash")
+        with open(filename, "w") as f:
+            f.write(commit)
+
+        # Reset self.config["tools"]["rust-root"]
+        self._rust_version = None
+        self.set_use_stable_rust(False)
+
+        self.fetch()
+
     @Command('fetch',
              description='Fetch Rust, Cargo and Cargo dependencies',
              category='devenv')
diff --git a/servo/rust-commit-hash b/servo/rust-commit-hash
index 978afb0be45f..04ac98844fd6 100644
--- a/servo/rust-commit-hash
+++ b/servo/rust-commit-hash
@@ -1 +1 @@
-5f13a3b540ab6024665322d716e487c800645f24
+23de823e93dc19ef1b9cb65b48860a892cd6ff18
\ No newline at end of file