diff --git a/compiler/gen/src/llvm/build.rs b/compiler/gen/src/llvm/build.rs
index 0218d8d584..e0c59b6c0c 100644
--- a/compiler/gen/src/llvm/build.rs
+++ b/compiler/gen/src/llvm/build.rs
@@ -24,6 +24,10 @@ const PRINT_FN_VERIFICATION_OUTPUT: bool = true;
 #[cfg(not(debug_assertions))]
 const PRINT_FN_VERIFICATION_OUTPUT: bool = false;
 
+// 0 is the C calling convention - see https://llvm.org/doxygen/namespacellvm_1_1CallingConv.html
+// TODO: experiment with different internal calling conventions, e.g. "fast"
+const DEFAULT_CALLING_CONVENTION: u32 = 0;
+
 type Scope<'a, 'ctx> = ImMap<Symbol, (Layout<'a>, PointerValue<'ctx>)>;
 
 pub struct Env<'a, 'ctx, 'env> {
@@ -211,6 +215,8 @@ pub fn build_expr<'a, 'ctx, 'env>(
                 }
             };
 
+            call.set_call_convention(DEFAULT_CALLING_CONVENTION);
+
             call.try_as_basic_value()
                 .left()
                 .unwrap_or_else(|| panic!("LLVM error: Invalid call by pointer."))
@@ -865,6 +871,8 @@ pub fn build_proc_header<'a, 'ctx, 'env>(
         Some(Linkage::Private),
     );
 
+    fn_val.set_call_conventions(DEFAULT_CALLING_CONVENTION);
+
     (fn_val, arg_basic_types)
 }
 
@@ -1103,6 +1111,8 @@ fn call_with_args<'a, 'ctx, 'env>(
                 .builder
                 .build_call(fn_val, arg_vals.into_bump_slice(), "call");
 
+            call.set_call_convention(DEFAULT_CALLING_CONVENTION);
+
             call.try_as_basic_value()
                 .left()
                 .unwrap_or_else(|| panic!("LLVM error: Invalid call by name for name {:?}", symbol))
diff --git a/compiler/gen/tests/test_gen.rs b/compiler/gen/tests/test_gen.rs
index a7f5fdb3f5..1aaf262f2b 100644
--- a/compiler/gen/tests/test_gen.rs
+++ b/compiler/gen/tests/test_gen.rs
@@ -31,6 +31,9 @@ mod test_gen {
     // Pointer size on current system
     const POINTER_SIZE: u32 = std::mem::size_of::<usize>() as u32;
 
+    // 0 is the C calling convention - see https://llvm.org/doxygen/namespacellvm_1_1CallingConv.html
+    const MAIN_CALLING_CONVENTION: u32 = 0;
+
     macro_rules! assert_llvm_evals_to {
         ($src:expr, $expected:expr, $ty:ty, $transform:expr) => {
             let arena = Bump::new();
@@ -128,6 +131,8 @@ mod test_gen {
             // Add main to the module.
             let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
 
+            main_fn.set_call_conventions(MAIN_CALLING_CONVENTION);
+
             // Add main's body
             let basic_block = context.append_basic_block(main_fn, "entry");
 
@@ -272,6 +277,8 @@ mod test_gen {
             // Add main to the module.
             let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
 
+            main_fn.set_call_conventions(MAIN_CALLING_CONVENTION);
+
             // Add main's body
             let basic_block = context.append_basic_block(main_fn, "entry");