diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b46b4a2..adcb724 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,7 +24,7 @@ jobs:
       - run: cargo fmt --all -- --check
         
   unit-tests:
-    name: Tests - ${{ matrix.os }} - ${{ matrix.toolchain }} - ${{ matrix.llvm[0] }}
+    name: Tests - ${{ matrix.os }} - ${{ matrix.toolchain }} - ${{ matrix.llvm[0] }} - ${{ matrix.features }}
     runs-on: ${{ matrix.os }}
     strategy:
         matrix:
@@ -37,13 +37,17 @@ jobs:
             - stable
           os:
             - ubuntu-latest
+          features:
+            - "rayon cranelift"
           include:
             - toolchain: stable
               os: windows-latest
               llvm: ""
+              features: "rayon cranelift"
             - toolchain: stable
               os: macos-latest
               llvm: ["16.0", "16-0"]
+              features: "rayon cranelift"
             #- toolchain: stable
             #  os: ubuntu-24.04-arm
             #  llvm: ["16.0", "16-0"]
@@ -53,9 +57,24 @@ jobs:
             - toolchain: beta
               os: ubuntu-latest
               llvm: ["16.0", "16-0"]
+              features: "rayon cranelift"
             - toolchain: nightly
               os: ubuntu-latest
               llvm: ["16.0", "16-0"]
+              features: "rayon cranelift"
+            - toolchain: stable
+              os: ubuntu-latest
+              llvm: ""
+              features: ""
+            - toolchain: stable
+              os: ubuntu-latest
+              llvm: ""
+              features: "rayon"
+            - toolchain: stable
+              os: ubuntu-latest
+              llvm: ""
+              features: "cranelift"
+
 
 
     steps:
@@ -67,14 +86,14 @@ jobs:
         path: |
           ${{ env.CARGO_HOME }}
           target
-        key: unit-test-${{ runner.os }}-${{ matrix.toolchain}}-${{ matrix.llvm }}
+        key: unit-test-${{ runner.os }}-${{ matrix.toolchain}}-${{ matrix.llvm }}-${{ matrix.features }}
     - name: Set up Rust
       run: rustup default ${{ matrix.toolchain }} && rustup update ${{ matrix.toolchain }} --no-self-update && rustup component add clippy rust-docs
     - name: Rust version
       run: rustc -Vv
     - name: Install LLVM and Clang
       uses: KyleMayes/install-llvm-action@v2
-      if : matrix.os == 'ubuntu-latest' || matrix.os == 'macos-latest' || matrix.os == 'ubuntu-24.04-arm'
+      if : matrix.llvm != '' && (matrix.os == 'ubuntu-latest' || matrix.os == 'macos-latest' || matrix.os == 'ubuntu-24.04-arm')
       with:
         version: ${{ matrix.llvm[0] }}
     - name: Install LLVM 16 (macos-13)
@@ -83,16 +102,16 @@ jobs:
         brew install llvm@16
     - name: Run tests (LLVM)
       if : matrix.llvm != ''
-      run: cargo test --verbose --features llvm${{ matrix.llvm[1] }} --features cranelift
+      run: cargo test --verbose --features llvm${{ matrix.llvm[1] }} --features "${{ matrix.features }}"
     - name: Run tests
       if : matrix.llvm == ''
-      run: cargo test --verbose --features cranelift
+      run: cargo test --verbose --features "${{ matrix.features }}"
     - name: Run Clippy (LLVM)
       if: matrix.toolchain == 'nightly'
-      run: cargo clippy --verbose --features llvm${{ matrix.llvm[1] }} --features cranelift
+      run: cargo clippy --verbose --features llvm${{ matrix.llvm[1] }} --features "${{ matrix.features }}"
     - name: Run Docs (LLVM)
       if: matrix.toolchain == 'nightly'
-      run: cargo rustdoc --features llvm${{ matrix.llvm[1] }} --features cranelift
+      run: cargo rustdoc --features llvm${{ matrix.llvm[1] }} --features "${{ matrix.features }}"
   book:
     runs-on: ubuntu-latest
     steps:
diff --git a/Cargo.toml b/Cargo.toml
index 6bc5bd5..e730f0e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,7 +11,7 @@ repository = "https://github.com/martinjrobins/diffsl"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
-default = ["rayon"]
+default = []
 llvm15-0 = ["inkwell-150", "llvm-sys-150", "llvm", "enzyme"]
 llvm16-0 = ["inkwell-160", "llvm-sys-160", "llvm", "enzyme"]
 llvm17-0 = ["inkwell-170", "llvm-sys-170", "llvm", "enzyme"]
diff --git a/src/execution/compiler.rs b/src/execution/compiler.rs
index 0911e58..7cf504e 100644
--- a/src/execution/compiler.rs
+++ b/src/execution/compiler.rs
@@ -257,6 +257,7 @@ impl<M: CodegenModule> Compiler<M> {
         }
     }
 
+    #[cfg(feature = "rayon")]
     fn with_threading<F>(&self, f: F)
     where
         F: Fn(u32, u32) + Sync + Send,
@@ -278,7 +279,13 @@ impl<M: CodegenModule> Compiler<M> {
         } else {
             f(0, 1);
         }
-        #[cfg(not(feature = "rayon"))]
+    }
+
+    #[cfg(not(feature = "rayon"))]
+    fn with_threading<F>(&self, f: F)
+    where
+        F: Fn(u32, u32),
+    {
         f(0, 1);
     }
 
@@ -864,15 +871,11 @@ impl<M: CodegenModule> Compiler<M> {
 mod tests {
     use crate::{
         discretise::DiscreteModel,
-        execution::module::{
-            CodegenModule, CodegenModuleCompile, CodegenModuleEmit, CodegenModuleJit,
-        },
+        execution::module::{CodegenModule, CodegenModuleCompile, CodegenModuleJit},
         parser::parse_ds_string,
         Compiler,
     };
     use approx::assert_relative_eq;
-    use std::io::Write;
-    use target_lexicon::triple;
 
     use super::CompilerMode;
 
@@ -1096,24 +1099,6 @@ mod tests {
         .unwrap();
     }
 
-    #[allow(dead_code)]
-    fn write_to_wasm<M: CodegenModuleCompile + CodegenModuleEmit>(
-        discrete_model: &DiscreteModel,
-        filename: &str,
-        mode: CompilerMode,
-    ) {
-        let module = M::from_discrete_model(
-            discrete_model,
-            mode,
-            Some(triple!("wasm32-unknown-unknown")),
-        )
-        .unwrap();
-        let buffer = module.to_object().unwrap();
-        let full_filename = format!("test_output/{filename}.wasm");
-        let mut file = std::fs::File::create(full_filename.as_str()).unwrap();
-        file.write_all(&buffer).unwrap();
-    }
-
     #[allow(dead_code)]
     fn tensor_test_common<T: CodegenModuleCompile + CodegenModuleJit>(
         discrete_model: &DiscreteModel,
@@ -1364,7 +1349,6 @@ mod tests {
                 #[cfg(feature = "llvm")]
                 {
                     use crate::execution::llvm::codegen::LlvmModule;
-                    write_to_wasm::<LlvmModule>(&discrete_model, concat!(stringify!($name),"_llvm"), CompilerMode::SingleThreaded);
                     let results = tensor_test_common::<LlvmModule>(&discrete_model, $tensor_name, CompilerMode::SingleThreaded);
                     assert_relative_eq!(results[0].as_slice(), $expected_value.as_slice());
                 }
@@ -1567,7 +1551,6 @@ mod tests {
                 #[cfg(feature = "llvm")]
                 {
                     use crate::execution::llvm::codegen::LlvmModule;
-                    write_to_wasm::<LlvmModule>(&discrete_model, concat!(stringify!($name),"_llvm"), CompilerMode::SingleThreaded);
                     let results = tensor_test_common::<LlvmModule>(&discrete_model, $tensor_name, CompilerMode::SingleThreaded);
                     assert_relative_eq!(results[1].as_slice(), $expected_grad.as_slice());
                     assert_relative_eq!(results[2].as_slice(), $expected_rgrad.as_slice());
@@ -1651,7 +1634,6 @@ mod tests {
                 #[cfg(feature = "llvm")]
                 {
                     use crate::execution::llvm::codegen::LlvmModule;
-                    write_to_wasm::<LlvmModule>(&discrete_model, concat!(stringify!($name),"_llvm"), CompilerMode::SingleThreaded);
                     let results = tensor_test_common::<LlvmModule>(&discrete_model, $tensor_name, CompilerMode::SingleThreaded);
                     assert_relative_eq!(results[0].as_slice(), $expected_value.as_slice());
                     assert_relative_eq!(results[1].as_slice(), $expected_grad.as_slice());
diff --git a/src/execution/module.rs b/src/execution/module.rs
index 96259ac..e67096c 100644
--- a/src/execution/module.rs
+++ b/src/execution/module.rs
@@ -7,8 +7,12 @@ use crate::discretise::DiscreteModel;
 
 use super::compiler::CompilerMode;
 
+#[cfg(feature = "rayon")]
 pub trait CodegenModule: Sized + Sync {}
 
+#[cfg(not(feature = "rayon"))]
+pub trait CodegenModule: Sized {}
+
 pub trait CodegenModuleCompile: CodegenModule {
     fn from_discrete_model(
         model: &DiscreteModel,