diff --git a/crates/anyref-xform/Cargo.toml b/crates/anyref-xform/Cargo.toml
index f1ae0802..d94f52e0 100644
--- a/crates/anyref-xform/Cargo.toml
+++ b/crates/anyref-xform/Cargo.toml
@@ -13,4 +13,4 @@ edition = '2018'
 
 [dependencies]
 failure = "0.1"
-walrus = "0.11.0"
+walrus = "0.12.0"
diff --git a/crates/cli-support/Cargo.toml b/crates/cli-support/Cargo.toml
index 2e88f03b..d510a25c 100644
--- a/crates/cli-support/Cargo.toml
+++ b/crates/cli-support/Cargo.toml
@@ -18,9 +18,9 @@ log = "0.4"
 rustc-demangle = "0.1.13"
 serde_json = "1.0"
 tempfile = "3.0"
-walrus = "0.11.0"
+walrus = "0.12.0"
 wasm-bindgen-anyref-xform = { path = '../anyref-xform', version = '=0.2.50' }
 wasm-bindgen-shared = { path = "../shared", version = '=0.2.50' }
 wasm-bindgen-threads-xform = { path = '../threads-xform', version = '=0.2.50' }
 wasm-bindgen-wasm-interpreter = { path = "../wasm-interpreter", version = '=0.2.50' }
-wasm-webidl-bindings = "0.4.0"
+wasm-webidl-bindings = "0.5.0"
diff --git a/crates/cli-support/src/lib.rs b/crates/cli-support/src/lib.rs
index 1e879d27..094079b2 100755
--- a/crates/cli-support/src/lib.rs
+++ b/crates/cli-support/src/lib.rs
@@ -539,7 +539,7 @@ impl Output {
             .join(wasm_name)
             .with_extension("wasm");
         fs::create_dir_all(out_dir)?;
-        let wasm_bytes = self.module.emit_wasm()?;
+        let wasm_bytes = self.module.emit_wasm();
         fs::write(&wasm_path, wasm_bytes)
             .with_context(|_| format!("failed to write `{}`", wasm_path.display()))?;
 
diff --git a/crates/cli-support/src/wasm2es6js.rs b/crates/cli-support/src/wasm2es6js.rs
index cdf8fa49..befff9d3 100644
--- a/crates/cli-support/src/wasm2es6js.rs
+++ b/crates/cli-support/src/wasm2es6js.rs
@@ -165,7 +165,7 @@ impl Output {
             imports = imports,
             set_exports = set_exports,
         );
-        let wasm = self.module.emit_wasm().expect("failed to serialize");
+        let wasm = self.module.emit_wasm();
         let (bytes, booted) = if self.base64 {
             (
                 format!(
diff --git a/crates/cli/Cargo.toml b/crates/cli/Cargo.toml
index 7bab7bda..7bedca83 100644
--- a/crates/cli/Cargo.toml
+++ b/crates/cli/Cargo.toml
@@ -24,7 +24,7 @@ rouille = { version = "3.0.0", default-features = false }
 serde = { version = "1.0", features = ['derive'] }
 serde_derive = "1.0"
 serde_json = "1.0"
-walrus = { version = "0.11.0", features = ['parallel'] }
+walrus = { version = "0.12.0", features = ['parallel'] }
 wasm-bindgen-cli-support = { path = "../cli-support", version = "=0.2.50" }
 wasm-bindgen-shared = { path = "../shared", version = "=0.2.50" }
 
diff --git a/crates/threads-xform/Cargo.toml b/crates/threads-xform/Cargo.toml
index 55847c83..0c405e73 100644
--- a/crates/threads-xform/Cargo.toml
+++ b/crates/threads-xform/Cargo.toml
@@ -13,4 +13,4 @@ edition = "2018"
 
 [dependencies]
 failure = "0.1"
-walrus = "0.11.0"
+walrus = "0.12.0"
diff --git a/crates/threads-xform/src/lib.rs b/crates/threads-xform/src/lib.rs
index f9ae5694..017d0728 100644
--- a/crates/threads-xform/src/lib.rs
+++ b/crates/threads-xform/src/lib.rs
@@ -388,8 +388,7 @@ fn inject_start(
     // nonzero (assuming we don't overflow...)
     body.local_get(local);
     body.if_else(
-        Box::new([]),
-        Box::new([]),
+        None,
         // If our thread id is nonzero then we're the second or greater thread, so
         // we give ourselves a stack via memory.grow and we update our stack
         // pointer as the default stack pointer is surely wrong for us.
@@ -401,7 +400,7 @@ fn inject_start(
                     .local_set(local);
 
                 // if local0 == -1 then trap
-                body.block(Box::new([]), Box::new([]), |body| {
+                body.block(None, |body| {
                     let target = body.id();
                     body.local_get(local)
                         .i32_const(-1)
diff --git a/crates/wasm-interpreter/Cargo.toml b/crates/wasm-interpreter/Cargo.toml
index d9466eb3..b935e4ed 100644
--- a/crates/wasm-interpreter/Cargo.toml
+++ b/crates/wasm-interpreter/Cargo.toml
@@ -14,7 +14,7 @@ edition = '2018'
 [dependencies]
 failure = "0.1"
 log = "0.4"
-walrus = "0.11.0"
+walrus = "0.12.0"
 
 [dev-dependencies]
 tempfile = "3"