diff --git a/.travis.yml b/.travis.yml
index ff4eca5336f..988b2393072 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -47,7 +47,7 @@ matrix:
         # Cargo has errors with sub-commands so ignore updating for now:
         - cargo --list | egrep "^\s*web$" -q || cargo install cargo-web
       script:
-        - cargo web test --target wasm32-unknown-unknown --nodejs
+        - cargo web test --target wasm32-unknown-unknown --nodejs --features=stdweb
     
     # Trust cross-built/emulated targets. We must repeat all non-default values.
     - rust: stable
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2c03338274d..8e473c892ad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ You may also find the [Update Guide](UPDATING.md) useful.
 - Deprecate `rand_derive`. (#256)
 - Add `log` feature. Logging is now available in `JitterRng`, `OsRng`, `EntropyRng` and `ReseedingRng`. (#246)
 - Add `serde-1` feature for some PRNGs. (#189)
+- `stdweb` feature for `OsRng` support on WASM via stdweb. (#272, #336)
 
 ### `Rng` trait
 - Split `Rng` in `RngCore` and `Rng` extension trait.
@@ -68,7 +69,7 @@ You may also find the [Update Guide](UPDATING.md) useful.
 ### Platform support and `OsRng`
 - Add support for CloudABI. (#224)
 - Remove support for NaCl. (#225)
-- Replace stubs with proper WASM support in `OsRng`. (#272)
+- WASM support for `OsRng` via stdweb, behind the `stdweb` feature. (#272, #336)
 - On systems that do not have a syscall interface, only keep a single file descriptor open for `OsRng`. (#239)
 - Better error handling and reporting in `OsRng` (using new error type). (#225)
 - `OsRng` now uses non-blocking when available. (#225)
diff --git a/Cargo.toml b/Cargo.toml
index 93ff76037d7..ae39a57187d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -39,9 +39,10 @@ winapi = { version = "0.3", features = ["minwindef", "ntsecapi", "profileapi", "
 rand_core = { path = 'rand_core', default-features = false }
 
 log = { version = "0.4", optional = true }
-
-serde = {version="1",optional=true}
+serde = {version="1", optional=true}
 serde_derive = {version="1", optional=true}
+stdweb = {version="0.4", optional=true}
+
 
 [workspace]
 members = ["rand_core"]
@@ -57,6 +58,3 @@ cloudabi = "0.0.3"
 
 [target.'cfg(target_os = "fuchsia")'.dependencies]
 fuchsia-zircon = "0.3.2"
-
-[target.wasm32-unknown-unknown.dependencies]
-stdweb = "0.4"
diff --git a/README.md b/README.md
index 311f8c3436e..09e91b99089 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,7 @@ optional features are available:
 -   `log` enables some logging via the `log` crate
 -   `nightly` enables all unstable features (`i128_support`)
 -   `serde-1` enables serialisation for some types, via Serde version 1
+-   `stdweb` enables support for `OsRng` on WASM via stdweb.
 -   `std` enabled by default; by setting "default-features = false" `no_std`
     mode is activated; this removes features depending on `std` functionality:
     -   `OsRng` is entirely unavailable
diff --git a/src/lib.rs b/src/lib.rs
index 292e72b88e2..00907f0b9e1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -179,7 +179,7 @@
 #![cfg_attr(not(feature="std"), no_std)]
 #![cfg_attr(all(feature="alloc", not(feature="std")), feature(alloc))]
 #![cfg_attr(feature = "i128_support", feature(i128_type, i128))]
-#![cfg_attr(all(target_arch = "wasm32", not(target_os = "emscripten")), recursion_limit="128")]
+#![cfg_attr(feature = "stdweb", recursion_limit="128")]
 
 #[cfg(feature="std")] extern crate std as core;
 #[cfg(all(feature = "alloc", not(feature="std")))] extern crate alloc;
@@ -188,7 +188,7 @@
 #[cfg(feature="serde-1")] extern crate serde;
 #[cfg(feature="serde-1")] #[macro_use] extern crate serde_derive;
 
-#[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+#[cfg(feature = "stdweb")]
 #[macro_use]
 extern crate stdweb;
 
diff --git a/src/os.rs b/src/os.rs
index 55269862341..7f59a975e37 100644
--- a/src/os.rs
+++ b/src/os.rs
@@ -613,7 +613,31 @@ mod imp {
     }
 }
 
-#[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+#[cfg(all(target_arch = "wasm32",
+          not(target_os = "emscripten"),
+          not(feature = "stdweb")))]
+mod imp {
+    use {Error, ErrorKind};
+
+    #[derive(Debug)]
+    pub struct OsRng;
+
+    impl OsRng {
+        pub fn new() -> Result<OsRng, Error> {
+            Err(Error::new(ErrorKind::Unavailable,
+                           "not supported on WASM without stdweb"))
+        }
+
+        pub fn try_fill_bytes(&mut self, _v: &mut [u8]) -> Result<(), Error> {
+            Err(Error::new(ErrorKind::Unavailable,
+                           "not supported on WASM without stdweb"))
+        }
+    }
+}
+
+#[cfg(all(target_arch = "wasm32",
+          not(target_os = "emscripten"),
+          feature = "stdweb"))]
 mod imp {
     use std::mem;
     use stdweb::unstable::TryInto;
diff --git a/src/thread_rng.rs b/src/thread_rng.rs
index 00e8604df5e..bc957a657ce 100644
--- a/src/thread_rng.rs
+++ b/src/thread_rng.rs
@@ -172,7 +172,7 @@ pub fn random<T>() -> T where Uniform: Distribution<T> {
 #[cfg(test)]
 mod test {
     #[test]
-    #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+    #[cfg(not(feature="stdweb"))]
     fn test_thread_rng() {
         use Rng;
         let mut r = ::thread_rng();