diff --git a/.travis.yml b/.travis.yml
index ca0e2d0..26d4978 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,16 +16,19 @@ matrix:
   include:
     - rust: nightly
       env: CLIPPY=y
+    - rust: stable
+      os: osx
+      env: WASMBIND=y
+    - rust: beta
+      os: osx
+      env: WASMBIND=y
 
 env:
   global:
     - LD_LIBRARY_PATH: /usr/local/lib
     - CLIPPY: n
 install:
-  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then source $HOME/.nvm/nvm.sh; fi
-  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then nvm install 10; fi
-  - if [ "$TRAVIS_OS_NAME" = "osx" ]; then nvm use 10; fi
-  - if [ "$TRAVIS_RUST_VERSION" != "1.13.0" ]; then curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh; fi
+  - if [ "$TRAVIS_OS_NAME" = "osx" ] && [ "$WASMBIND" = "y" ] ; then source ./ci/install-node.sh; fi
 script: ./ci/travis.sh
 notifications:
   email: false
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 108f9f0..0c8b941 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,15 @@ Chrono obeys the principle of [Semantic Versioning](http://semver.org/).
 There were/are numerous minor versions before 1.0 due to the language changes.
 Versions with only mechanical changes will be omitted from the following list.
 
+## 0.4.9
+
+### Fixes
+
+* Make Datetime arithmatic adjust their offsets after discovering their new
+  timestamps (@quodlibetor #337)
+* Put wasm-bindgen related code and dependencies behind a `wasmbind` feature
+  gate. (@quodlibetor #335)
+
 ## 0.4.8
 
 ### Fixes
diff --git a/Cargo.toml b/Cargo.toml
index ecb2dcf..4ef98fb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -26,6 +26,7 @@ name = "chrono"
 [features]
 default = ["clock"]
 clock = ["time"]
+wasmbind = ["wasm-bindgen", "js-sys"]
 
 [dependencies]
 libc = { version = "0.2", default-features = false }
@@ -35,10 +36,9 @@ num-traits = { version = "0.2", default-features = false }
 rustc-serialize = { version = "0.3.20", optional = true }
 serde = { version = "1", optional = true }
 
-
 [target.'cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))'.dependencies]
-wasm-bindgen = { version = "0.2" }
-js-sys = "0.3" # contains FFI bindings for the JS Date API
+wasm-bindgen = { version = "0.2", optional = true }
+js-sys = { version = "0.3", optional = true } # contains FFI bindings for the JS Date API
 
 [dev-dependencies]
 serde_json = { version = "1" }
diff --git a/ci/install-node.sh b/ci/install-node.sh
new file mode 100644
index 0000000..65318b3
--- /dev/null
+++ b/ci/install-node.sh
@@ -0,0 +1,8 @@
+#!/usr/bin/env sh
+
+echo "installing node via nvm"
+
+source "$HOME/.nvm/nvm.sh"
+nvm install 10
+nvm use 10
+curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
diff --git a/ci/travis.sh b/ci/travis.sh
index 2747fee..04dfe83 100755
--- a/ci/travis.sh
+++ b/ci/travis.sh
@@ -29,6 +29,21 @@ build_and_test() {
   # also vary the local time zone to (hopefully) catch tz-dependent bugs
   # also avoid doc-testing multiple times---it takes a lot and rarely helps
   cargo clean
+
+  if [ "${WASMBIND}" != "y" ]; then
+      build_and_test_nonwasm
+  else
+      build_and_test_wasm
+  fi
+
+  if [[ "$CHANNEL" == stable ]]; then
+      if [[ -n "$TRAVIS" ]] ; then
+          check_readme
+      fi
+  fi
+}
+
+build_and_test_nonwasm() {
   channel build -v
   TZ=ACST-9:30 channel test -v --lib
   channel build -v --features rustc-serialize
@@ -47,9 +62,11 @@ build_and_test() {
   TZ=UTC0 channel test -v --no-default-features --features serde --lib
   channel build -v --no-default-features --features serde,rustc-serialize
   TZ=Asia/Katmandu channel test -v --no-default-features --features serde,rustc-serialize --lib
+}
+
+build_and_test_wasm() {
+    channel build --features wasmbind -v
 
-  if [ -n "${TRAVIS}" ] && [ "${TRAVIS_RUST_VERSION}" != "1.13.0" ]; then
-    # wasm tests
     touch tests/wasm.rs # ensure rebuild happens so TZ / NOW take effect
     TZ=ACST-9:30 NOW=$(date +%s) wasm-pack test --node
     touch tests/wasm.rs
@@ -58,13 +75,6 @@ build_and_test() {
     TZ=UTC0 NOW=$(date +%s) wasm-pack test --node
     touch tests/wasm.rs
     TZ=Asia/Katmandu NOW=$(date +%s) wasm-pack test --node
-  fi
-
-  if [[ "$CHANNEL" == stable ]]; then
-      if [[ -n "$TRAVIS" ]] ; then
-          check_readme
-      fi
-  fi
 }
 
 build_only() {
diff --git a/src/lib.rs b/src/lib.rs
index 2962e65..b43fa0d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -414,9 +414,9 @@ extern crate serde as serdelib;
 #[cfg(test)]
 #[macro_use]
 extern crate doc_comment;
-#[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+#[cfg(all(target_arch = "wasm32", feature="wasmbind"))]
 extern crate wasm_bindgen;
-#[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+#[cfg(all(target_arch = "wasm32", feature="wasmbind"))]
 extern crate js_sys;
 
 #[cfg(test)]
diff --git a/src/offset/local.rs b/src/offset/local.rs
index 68c27c4..70c01e6 100644
--- a/src/offset/local.rs
+++ b/src/offset/local.rs
@@ -87,13 +87,13 @@ impl Local {
     }
 
     /// Returns a `DateTime` which corresponds to the current date.
-    #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+    #[cfg(not(all(target_arch = "wasm32", feature = "wasmbind")))]
     pub fn now() -> DateTime<Local> {
         tm_to_datetime(oldtime::now())
     }
 
     /// Returns a `DateTime` which corresponds to the current date.
-    #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+    #[cfg(all(target_arch = "wasm32", feature = "wasmbind"))]
     pub fn now() -> DateTime<Local> {
         use super::Utc;
         let now: DateTime<Utc> = super::Utc::now();
diff --git a/src/offset/utc.rs b/src/offset/utc.rs
index 36f4e5f..87a4fba 100644
--- a/src/offset/utc.rs
+++ b/src/offset/utc.rs
@@ -4,7 +4,7 @@
 //! The UTC (Coordinated Universal Time) time zone.
 
 use std::fmt;
-#[cfg(all(feature="clock", not(all(target_arch = "wasm32", not(target_os = "emscripten")))))]
+#[cfg(all(feature="clock", not(all(target_arch = "wasm32", feature = "wasmbind"))))]
 use oldtime;
 
 use naive::{NaiveDate, NaiveDateTime};
@@ -38,7 +38,7 @@ impl Utc {
     pub fn today() -> Date<Utc> { Utc::now().date() }
 
     /// Returns a `DateTime` which corresponds to the current date.
-    #[cfg(not(all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+    #[cfg(not(all(target_arch = "wasm32", feature = "wasmbind")))]
     pub fn now() -> DateTime<Utc> {
         let spec = oldtime::get_time();
         let naive = NaiveDateTime::from_timestamp(spec.sec, spec.nsec as u32);
@@ -46,7 +46,7 @@ impl Utc {
     }
 
     /// Returns a `DateTime` which corresponds to the current date.
-    #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+    #[cfg(all(target_arch = "wasm32", feature = "wasmbind"))]
     pub fn now() -> DateTime<Utc> {
         let now = js_sys::Date::new_0();
         let millisecs_since_unix_epoch: u64 = now.get_time() as u64;
diff --git a/tests/wasm.rs b/tests/wasm.rs
index b95d9f0..e125372 100644
--- a/tests/wasm.rs
+++ b/tests/wasm.rs
@@ -1,4 +1,4 @@
-#[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
+#[cfg(all(target_arch = "wasm32", feature = "wasmbind"))]
 mod test {
     extern crate chrono;
     extern crate wasm_bindgen_test;