diff --git a/Cargo.lock b/Cargo.lock
index 9744bd7d076e..c096d3c84e8a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -8980,8 +8980,7 @@ dependencies = [
 [[package]]
 name = "wasmer"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "063315805273d66057de5e7145919e745134374ee9a2acfeb354814a2240649e"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#2e48e6bc7b220558d854f3b512d62292e3e0c263"
 dependencies = [
  "bytes",
  "cfg-if",
@@ -9011,8 +9010,7 @@ dependencies = [
 [[package]]
 name = "wasmer-compiler"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f809637584d1ba52e43291703c255107f87858b7fc70d78b4bebc175f462f5d9"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#2e48e6bc7b220558d854f3b512d62292e3e0c263"
 dependencies = [
  "backtrace",
  "bytes",
@@ -9038,8 +9036,7 @@ dependencies = [
 [[package]]
 name = "wasmer-compiler-cranelift"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "17b092fd256db30f3ffe069173c7799bde50283a0969827e034004ae755d4fe8"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#2e48e6bc7b220558d854f3b512d62292e3e0c263"
 dependencies = [
  "cranelift-codegen 0.91.1",
  "cranelift-entity 0.91.1",
@@ -9057,8 +9054,7 @@ dependencies = [
 [[package]]
 name = "wasmer-compiler-singlepass"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6852aef78618c839d02874283cdc331beb91e01727789c29007920ff3803c915"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#2e48e6bc7b220558d854f3b512d62292e3e0c263"
 dependencies = [
  "byteorder",
  "dynasm",
@@ -9076,8 +9072,7 @@ dependencies = [
 [[package]]
 name = "wasmer-derive"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d7f14f05a6665e0a4fcdfced554b1b9bc649b8a411414a2c99802c6daa3faed3"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#2e48e6bc7b220558d854f3b512d62292e3e0c263"
 dependencies = [
  "proc-macro-error 1.0.4",
  "proc-macro2",
@@ -9088,8 +9083,7 @@ dependencies = [
 [[package]]
 name = "wasmer-types"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "60b718632586b3e2959435adabb1b449a8632ee50ff086058df2708878eb774b"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#2e48e6bc7b220558d854f3b512d62292e3e0c263"
 dependencies = [
  "bytecheck",
  "enum-iterator",
@@ -9104,8 +9098,7 @@ dependencies = [
 [[package]]
 name = "wasmer-vm"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f6e3747c71e2dd938cdf90c735f37dc72cbb8538109b4a134d719a64826ae5c2"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#2e48e6bc7b220558d854f3b512d62292e3e0c263"
 dependencies = [
  "backtrace",
  "cc",
diff --git a/Cargo.toml b/Cargo.toml
index ec2ef8eaca53..35715c5929cd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -215,3 +215,8 @@ opt-level = 3
 version = "0.4.1"
 git = "https://github.com/Twey/rust-indexed-db"
 branch = "no-uuid-wasm-bindgen"
+
+[patch.crates-io.wasmer]
+version = "4.3.0-alpha.1"
+git = "https://github.com/Twey/wasmer"
+branch = "non-send-environments"
diff --git a/examples/Cargo.lock b/examples/Cargo.lock
index 0538fe390832..aa0f43c8bc35 100644
--- a/examples/Cargo.lock
+++ b/examples/Cargo.lock
@@ -4952,8 +4952,7 @@ dependencies = [
 [[package]]
 name = "wasmer"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "063315805273d66057de5e7145919e745134374ee9a2acfeb354814a2240649e"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#22d085d25f1b1141d22b22938163541efe34cbe7"
 dependencies = [
  "bytes",
  "cfg-if",
@@ -4982,8 +4981,7 @@ dependencies = [
 [[package]]
 name = "wasmer-compiler"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f809637584d1ba52e43291703c255107f87858b7fc70d78b4bebc175f462f5d9"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#22d085d25f1b1141d22b22938163541efe34cbe7"
 dependencies = [
  "backtrace",
  "bytes",
@@ -5009,8 +5007,7 @@ dependencies = [
 [[package]]
 name = "wasmer-compiler-cranelift"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "17b092fd256db30f3ffe069173c7799bde50283a0969827e034004ae755d4fe8"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#22d085d25f1b1141d22b22938163541efe34cbe7"
 dependencies = [
  "cranelift-codegen 0.91.1",
  "cranelift-entity 0.91.1",
@@ -5028,8 +5025,7 @@ dependencies = [
 [[package]]
 name = "wasmer-compiler-singlepass"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6852aef78618c839d02874283cdc331beb91e01727789c29007920ff3803c915"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#22d085d25f1b1141d22b22938163541efe34cbe7"
 dependencies = [
  "byteorder",
  "dynasm",
@@ -5047,8 +5043,7 @@ dependencies = [
 [[package]]
 name = "wasmer-derive"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d7f14f05a6665e0a4fcdfced554b1b9bc649b8a411414a2c99802c6daa3faed3"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#22d085d25f1b1141d22b22938163541efe34cbe7"
 dependencies = [
  "proc-macro-error 1.0.4",
  "proc-macro2",
@@ -5059,8 +5054,7 @@ dependencies = [
 [[package]]
 name = "wasmer-types"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "60b718632586b3e2959435adabb1b449a8632ee50ff086058df2708878eb774b"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#22d085d25f1b1141d22b22938163541efe34cbe7"
 dependencies = [
  "bytecheck",
  "enum-iterator",
@@ -5075,8 +5069,7 @@ dependencies = [
 [[package]]
 name = "wasmer-vm"
 version = "4.3.0-alpha.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f6e3747c71e2dd938cdf90c735f37dc72cbb8538109b4a134d719a64826ae5c2"
+source = "git+https://github.com/Twey/wasmer?branch=non-send-environments#22d085d25f1b1141d22b22938163541efe34cbe7"
 dependencies = [
  "backtrace",
  "cc",
diff --git a/examples/Cargo.toml b/examples/Cargo.toml
index 4dfeb6beb6eb..9293c8e50dac 100644
--- a/examples/Cargo.toml
+++ b/examples/Cargo.toml
@@ -52,3 +52,8 @@ strip = 'debuginfo'
 
 [profile.bench]
 debug = true
+
+[patch.crates-io.wasmer]
+version = "4.3.0-alpha.1"
+git = "https://github.com/Twey/wasmer"
+branch = "non-send-environments"
diff --git a/linera-execution/Cargo.toml b/linera-execution/Cargo.toml
index 4f2b0cbf12ad..072ec7c6a5ef 100644
--- a/linera-execution/Cargo.toml
+++ b/linera-execution/Cargo.toml
@@ -88,3 +88,8 @@ cfg_aliases.workspace = true
 
 [package.metadata.cargo-machete]
 ignored = ["serde_bytes"]
+
+[patch.crates-io.wasmer]
+version = "4.3.0-alpha.1"
+git = "https://github.com/Twey/wasmer"
+branch = "non-send-environments"
diff --git a/linera-execution/src/lib.rs b/linera-execution/src/lib.rs
index fd76fedc931d..c9f8a37b74f6 100644
--- a/linera-execution/src/lib.rs
+++ b/linera-execution/src/lib.rs
@@ -69,10 +69,10 @@ pub type UserContractCode = Arc<dyn UserContractModule + Send + Sync + 'static>;
 pub type UserServiceCode = Arc<dyn UserServiceModule + Send + Sync + 'static>;
 
 /// An implementation of [`UserContract`].
-pub type UserContractInstance = Box<dyn UserContract + Send + Sync + 'static>;
+pub type UserContractInstance = Box<dyn UserContract + 'static>;
 
 /// An implementation of [`UserService`].
-pub type UserServiceInstance = Box<dyn UserService + Send + Sync + 'static>;
+pub type UserServiceInstance = Box<dyn UserService + 'static>;
 
 /// A factory trait to obtain a [`UserContract`] from a [`UserContractModule`]
 pub trait UserContractModule {
diff --git a/linera-execution/src/test_utils/mock_application.rs b/linera-execution/src/test_utils/mock_application.rs
index 8d8ee4345e66..353fa4ec2db0 100644
--- a/linera-execution/src/test_utils/mock_application.rs
+++ b/linera-execution/src/test_utils/mock_application.rs
@@ -195,7 +195,7 @@ impl UserContractModule for MockApplication {
     fn instantiate(
         &self,
         runtime: ContractSyncRuntime,
-    ) -> Result<Box<dyn UserContract + Send + Sync + 'static>, ExecutionError> {
+    ) -> Result<Box<dyn UserContract + 'static>, ExecutionError> {
         Ok(Box::new(self.create_mock_instance(runtime)))
     }
 }
@@ -204,7 +204,7 @@ impl UserServiceModule for MockApplication {
     fn instantiate(
         &self,
         runtime: ServiceSyncRuntime,
-    ) -> Result<Box<dyn UserService + Send + Sync + 'static>, ExecutionError> {
+    ) -> Result<Box<dyn UserService + 'static>, ExecutionError> {
         Ok(Box::new(self.create_mock_instance(runtime)))
     }
 }
diff --git a/linera-execution/src/wasm/system_api.rs b/linera-execution/src/wasm/system_api.rs
index 56e1e6a381e6..3a178ad79193 100644
--- a/linera-execution/src/wasm/system_api.rs
+++ b/linera-execution/src/wasm/system_api.rs
@@ -79,7 +79,7 @@ pub struct ContractSystemApi<Caller>(PhantomData<Caller>);
 impl<Caller, Runtime> ContractSystemApi<Caller>
 where
     Caller: Instance<UserData = SystemApiData<Runtime>>,
-    Runtime: ContractRuntime + Send + 'static,
+    Runtime: ContractRuntime + 'static,
 {
     /// Returns the ID of the current chain.
     fn get_chain_id(caller: &mut Caller) -> Result<ChainId, RuntimeError> {
@@ -354,7 +354,7 @@ pub struct ServiceSystemApi<Caller>(PhantomData<Caller>);
 impl<Caller, Runtime> ServiceSystemApi<Caller>
 where
     Caller: Instance<UserData = SystemApiData<Runtime>>,
-    Runtime: ServiceRuntime + Send + 'static,
+    Runtime: ServiceRuntime + 'static,
 {
     /// Returns the ID of the current chain.
     fn get_chain_id(caller: &mut Caller) -> Result<ChainId, RuntimeError> {
@@ -503,7 +503,7 @@ pub struct ViewSystemApi<Caller>(PhantomData<Caller>);
 impl<Caller, Runtime> ViewSystemApi<Caller>
 where
     Caller: Instance<UserData = SystemApiData<Runtime>>,
-    Runtime: BaseRuntime + WriteBatch + Send + 'static,
+    Runtime: BaseRuntime + WriteBatch + 'static,
 {
     /// Creates a new promise to check if the `key` is in storage.
     fn contains_key_new(caller: &mut Caller, key: Vec<u8>) -> Result<u32, RuntimeError> {
diff --git a/linera-execution/src/wasm/wasmer.rs b/linera-execution/src/wasm/wasmer.rs
index fc72c2ab585d..15324f1283ee 100644
--- a/linera-execution/src/wasm/wasmer.rs
+++ b/linera-execution/src/wasm/wasmer.rs
@@ -26,13 +26,6 @@ use crate::{
     QueryContext, ServiceRuntime,
 };
 
-#[cfg(not(web))]
-use {
-    wasmer::sys::EngineBuilder,
-    wasmer::Cranelift,
-    wasmer::Singlepass,
-};
-
 /// An [`Engine`] instance configured to run application services.
 static SERVICE_ENGINE: Lazy<Engine> = Lazy::new(|| {
     #[cfg(web)]
@@ -79,7 +72,7 @@ impl WasmContractModule {
 
 impl<Runtime> WasmerContractInstance<Runtime>
 where
-    Runtime: ContractRuntime + WriteBatch + Clone + Send + Sync + Unpin + 'static,
+    Runtime: ContractRuntime + WriteBatch + Clone + Unpin + 'static,
 {
     /// Prepares a runtime instance to call into the Wasm contract.
     pub fn prepare(
@@ -114,7 +107,7 @@ impl WasmServiceModule {
 
 impl<Runtime> WasmerServiceInstance<Runtime>
 where
-    Runtime: ServiceRuntime + WriteBatch + Clone + Send + Sync + Unpin + 'static,
+    Runtime: ServiceRuntime + WriteBatch + Clone + Unpin + 'static,
 {
     /// Prepares a runtime instance to call into the Wasm service.
     pub fn prepare(service_module: &Module, runtime: Runtime) -> Result<Self, WasmExecutionError> {
@@ -132,7 +125,7 @@ where
 
 impl<Runtime> crate::UserContract for WasmerContractInstance<Runtime>
 where
-    Runtime: ContractRuntime + Send + Unpin + 'static,
+    Runtime: ContractRuntime + Unpin + 'static,
 {
     fn instantiate(
         &mut self,
@@ -174,10 +167,7 @@ where
     }
 }
 
-impl<Runtime> crate::UserService for WasmerServiceInstance<Runtime>
-where
-    Runtime: Send + 'static,
-{
+impl<Runtime: 'static> crate::UserService for WasmerServiceInstance<Runtime> {
     fn handle_query(
         &mut self,
         _context: QueryContext,
diff --git a/linera-witty/src/runtime/wasmer/export_function.rs b/linera-witty/src/runtime/wasmer/export_function.rs
index e0a50129fbf6..854fe77113f3 100644
--- a/linera-witty/src/runtime/wasmer/export_function.rs
+++ b/linera-witty/src/runtime/wasmer/export_function.rs
@@ -20,7 +20,7 @@ macro_rules! export_function {
         where
             $( $types: FromToNativeWasmType, )*
             FlatResult: MaybeFlatType + WasmTypeList,
-            UserData: Send + 'static,
+            UserData: 'static,
             HandlerError: Error + Send + Sync + 'static,
             Handler:
                 Fn(
diff --git a/linera-witty/src/runtime/wasmer/function.rs b/linera-witty/src/runtime/wasmer/function.rs
index 42f26a057a62..22ae608dbafb 100644
--- a/linera-witty/src/runtime/wasmer/function.rs
+++ b/linera-witty/src/runtime/wasmer/function.rs
@@ -32,7 +32,7 @@ macro_rules! impl_instance_with_function_for {
         where
             $( $types: FlatType + FromToNativeWasmType + NativeWasmTypeInto, )*
             Results: FlatLayout + WasmerResults,
-            UserData: Send + 'static,
+            UserData: 'static,
         {
             type Function = TypedFunction<
                 <HList![$( $types ),*] as WasmerParameters>::ImportParameters,
diff --git a/linera-witty/src/runtime/wasmer/memory.rs b/linera-witty/src/runtime/wasmer/memory.rs
index 840a10282739..f1df6f475ac3 100644
--- a/linera-witty/src/runtime/wasmer/memory.rs
+++ b/linera-witty/src/runtime/wasmer/memory.rs
@@ -12,10 +12,7 @@ use crate::{GuestPointer, RuntimeError, RuntimeMemory};
 
 macro_rules! impl_memory_traits {
     ($instance:ty) => {
-        impl<UserData> InstanceWithMemory for $instance
-        where
-            UserData: Send + 'static,
-        {
+        impl<UserData: 'static> InstanceWithMemory for $instance {
             fn memory_from_export(&self, export: Extern) -> Result<Option<Memory>, RuntimeError> {
                 Ok(match export {
                     Extern::Memory(memory) => Some(memory),
@@ -24,10 +21,7 @@ macro_rules! impl_memory_traits {
             }
         }
 
-        impl<UserData> RuntimeMemory<$instance> for Memory
-        where
-            UserData: Send + 'static,
-        {
+        impl<UserData: 'static> RuntimeMemory<$instance> for Memory {
             fn read<'instance>(
                 &self,
                 instance: &'instance $instance,
diff --git a/linera-witty/src/runtime/wasmer/mod.rs b/linera-witty/src/runtime/wasmer/mod.rs
index 08b6e4ef8e47..cfb572592481 100644
--- a/linera-witty/src/runtime/wasmer/mod.rs
+++ b/linera-witty/src/runtime/wasmer/mod.rs
@@ -35,10 +35,7 @@ pub struct InstanceBuilder<UserData> {
     environment: Environment<UserData>,
 }
 
-impl<UserData> InstanceBuilder<UserData>
-where
-    UserData: Send + 'static,
-{
+impl<UserData: 'static> InstanceBuilder<UserData> {
     /// Creates a new [`InstanceBuilder`].
     pub fn new(engine: Engine, user_data: UserData) -> Self {
         InstanceBuilder {
@@ -160,10 +157,7 @@ impl<UserData> Instance for EntrypointInstance<UserData> {
 /// guest.
 pub type ReentrantInstance<'a, UserData> = FunctionEnvMut<'a, Environment<UserData>>;
 
-impl<UserData> Instance for ReentrantInstance<'_, UserData>
-where
-    UserData: Send + 'static,
-{
+impl<UserData: 'static> Instance for ReentrantInstance<'_, UserData> {
     type Runtime = Wasmer;
     type UserData = UserData;
     type UserDataReference<'a> = MutexGuard<'a, UserData>