diff --git a/compiler/gen_wasm/src/lib.rs b/compiler/gen_wasm/src/lib.rs
index 7cca526acb..50f1e81350 100644
--- a/compiler/gen_wasm/src/lib.rs
+++ b/compiler/gen_wasm/src/lib.rs
@@ -264,5 +264,5 @@ pub const DEBUG_LOG_SETTINGS: WasmDebugLogSettings = WasmDebugLogSettings {
     let_stmt_ir: false && cfg!(debug_assertions),
     instructions: false && cfg!(debug_assertions),
     storage_map: false && cfg!(debug_assertions),
-    keep_test_binary: false && cfg!(debug_assertions),
+    keep_test_binary: true && cfg!(debug_assertions),
 };
diff --git a/compiler/gen_wasm/src/low_level.rs b/compiler/gen_wasm/src/low_level.rs
index b396a83adc..281e1d204d 100644
--- a/compiler/gen_wasm/src/low_level.rs
+++ b/compiler/gen_wasm/src/low_level.rs
@@ -1028,7 +1028,7 @@ pub fn call_higher_order_lowlevel<'a>(
                     Layout::Builtin(Builtin::List(elem_x)),
                     Layout::Builtin(Builtin::List(elem_ret)),
                 ) => (elem_x, elem_ret),
-                _ => unreachable!("invalid arguments layout for {:?}", op),
+                _ => internal_error!("invalid arguments layout for {:?}", op),
             };
             let elem_x_size = elem_x.stack_size(TARGET_INFO);
             let (elem_ret_size, elem_ret_align) = elem_ret.stack_size_and_alignment(TARGET_INFO);
@@ -1071,7 +1071,7 @@ pub fn call_higher_order_lowlevel<'a>(
                     Layout::Builtin(Builtin::List(y)),
                     Layout::Builtin(Builtin::List(ret)),
                 ) => (x, y, ret),
-                _ => unreachable!("invalid arguments layout for {:?}", op),
+                _ => internal_error!("invalid arguments layout for {:?}", op),
             };
             let elem_x_size = elem_x.stack_size(TARGET_INFO);
             let elem_y_size = elem_y.stack_size(TARGET_INFO);
@@ -1124,8 +1124,80 @@ pub fn call_higher_order_lowlevel<'a>(
             );
         }
 
-        ListMap3 { .. }
-        | ListMap4 { .. }
+        ListMap3 { xs, ys, zs } => {
+            let list_x = backend.storage.symbol_layouts[xs];
+            let list_y = backend.storage.symbol_layouts[ys];
+            let list_z = backend.storage.symbol_layouts[zs];
+
+            let (elem_x, elem_y, elem_z, elem_ret) = match (list_x, list_y, list_z, return_layout) {
+                (
+                    Layout::Builtin(Builtin::List(x)),
+                    Layout::Builtin(Builtin::List(y)),
+                    Layout::Builtin(Builtin::List(z)),
+                    Layout::Builtin(Builtin::List(ret)),
+                ) => (x, y, z, ret),
+                e => internal_error!("invalid arguments layout for {:?}\n{:?}", op, e),
+            };
+            let elem_x_size = elem_x.stack_size(TARGET_INFO);
+            let elem_y_size = elem_y.stack_size(TARGET_INFO);
+            let elem_z_size = elem_y.stack_size(TARGET_INFO);
+            let (elem_ret_size, elem_ret_align) = elem_ret.stack_size_and_alignment(TARGET_INFO);
+
+            let dec_x_fn_ptr = backend.get_refcount_fn_ptr(*elem_x, HelperOp::Dec);
+            let dec_y_fn_ptr = backend.get_refcount_fn_ptr(*elem_y, HelperOp::Dec);
+            let dec_z_fn_ptr = backend.get_refcount_fn_ptr(*elem_z, HelperOp::Dec);
+
+            let cb = &mut backend.code_builder;
+
+            /* Load Wasm arguments
+                return ptr              i32
+                list1: RocList,         i64, i64
+                list2: RocList,         i64, i64
+                list3: RocList,         i64, i64
+                caller: Caller3,        i32
+                data: Opaque,           i32
+                inc_n_data: IncN,       i32
+                data_is_owned: bool,    i32
+                alignment: u32,         i32
+                a_width: usize,         i32
+                b_width: usize,         i32
+                c_width: usize,         i32
+                d_width: usize,         i32
+                dec_a: Dec,             i32
+                dec_b: Dec,             i32
+                dec_c: Dec,             i32
+            */
+            backend.storage.load_symbols(cb, &[return_sym]);
+            backend.storage.load_symbol_zig(cb, *xs);
+            backend.storage.load_symbol_zig(cb, *ys);
+            backend.storage.load_symbol_zig(cb, *zs);
+            cb.i32_const(wrapper_fn_ptr);
+            if closure_data_exists {
+                backend.storage.load_symbols(cb, &[*captured_environment]);
+            } else {
+                cb.i32_const(0); // null pointer
+            }
+            cb.i32_const(inc_fn_ptr);
+            cb.i32_const(*owns_captured_environment as i32);
+            cb.i32_const(elem_ret_align as i32);
+            cb.i32_const(elem_x_size as i32);
+            cb.i32_const(elem_y_size as i32);
+            cb.i32_const(elem_z_size as i32);
+            cb.i32_const(elem_ret_size as i32);
+            cb.i32_const(dec_x_fn_ptr);
+            cb.i32_const(dec_y_fn_ptr);
+            cb.i32_const(dec_z_fn_ptr);
+
+            let num_wasm_args = 19;
+            let has_return_val = false;
+            backend.call_zig_builtin_after_loading_args(
+                bitcode::LIST_MAP3,
+                num_wasm_args,
+                has_return_val,
+            );
+        }
+
+        ListMap4 { .. }
         | ListMapWithIndex { .. }
         | ListKeepIf { .. }
         | ListWalk { .. }
diff --git a/compiler/test_gen/src/gen_list.rs b/compiler/test_gen/src/gen_list.rs
index 92ab071fa2..74ad1281b2 100644
--- a/compiler/test_gen/src/gen_list.rs
+++ b/compiler/test_gen/src/gen_list.rs
@@ -1137,7 +1137,7 @@ fn list_map4_different_length() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_map3_group() {
     assert_evals_to!(
         indoc!(
@@ -1151,7 +1151,7 @@ fn list_map3_group() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_map3_different_length() {
     assert_evals_to!(
         indoc!(