diff --git a/compiler/can/src/builtins.rs b/compiler/can/src/builtins.rs
index 8e94860706..e2d7b7cea4 100644
--- a/compiler/can/src/builtins.rs
+++ b/compiler/can/src/builtins.rs
@@ -960,7 +960,7 @@ fn list_walk_right(symbol: Symbol, var_store: &mut VarStore) -> Def {
             (func_var, Var(Symbol::ARG_2)),
             (accum_var, Var(Symbol::ARG_3)),
         ],
-        ret_var: list_var,
+        ret_var: accum_var,
     };
 
     defn(
@@ -972,7 +972,7 @@ fn list_walk_right(symbol: Symbol, var_store: &mut VarStore) -> Def {
         ],
         var_store,
         body,
-        list_var,
+        accum_var,
     )
 }
 
diff --git a/compiler/gen/src/llvm/build.rs b/compiler/gen/src/llvm/build.rs
index b1fc1f23a9..e95e2e562a 100644
--- a/compiler/gen/src/llvm/build.rs
+++ b/compiler/gen/src/llvm/build.rs
@@ -1711,7 +1711,22 @@ fn run_low_level<'a, 'ctx, 'env>(
             // List.walkRight : List elem, (elem -> accum -> accum), accum -> accum
             debug_assert_eq!(args.len(), 3);
 
-            list_walk_right(env)
+            let (list, list_layout) = load_symbol_and_layout(env, scope, &args[0]);
+
+            let (func, func_layout) = load_symbol_and_layout(env, scope, &args[1]);
+
+            let (default, default_layout) = load_symbol_and_layout(env, scope, &args[2]);
+
+            list_walk_right(
+                env,
+                parent,
+                list,
+                list_layout,
+                func,
+                func_layout,
+                default,
+                default_layout,
+            )
         }
         ListAppend => {
             // List.append : List elem, elem -> List elem
diff --git a/compiler/gen/src/llvm/build_list.rs b/compiler/gen/src/llvm/build_list.rs
index bd53ad0e04..deb55373dd 100644
--- a/compiler/gen/src/llvm/build_list.rs
+++ b/compiler/gen/src/llvm/build_list.rs
@@ -642,10 +642,96 @@ pub fn list_len<'ctx>(
 }
 
 /// List.walkRight : List elem, (elem -> accum -> accum), accum -> accum
-pub fn list_walk_right<'a, 'ctx, 'env>(env: &Env<'a, 'ctx, 'env>) -> BasicValueEnum<'ctx> {
+#[allow(clippy::too_many_arguments)]
+pub fn list_walk_right<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    parent: FunctionValue<'ctx>,
+    list: BasicValueEnum<'ctx>,
+    list_layout: &Layout<'a>,
+    func: BasicValueEnum<'ctx>,
+    func_layout: &Layout<'a>,
+    default: BasicValueEnum<'ctx>,
+    default_layout: &Layout<'a>,
+) -> BasicValueEnum<'ctx> {
     let ctx = env.context;
+    let builder = env.builder;
 
-    BasicValueEnum::IntValue(ctx.i64_type().const_int(0 as u64, false))
+    let list_wrapper = list.into_struct_value();
+    let len = list_len(env.builder, list_wrapper);
+
+    let accum_type = basic_type_from_layout(env.arena, ctx, default_layout, env.ptr_bytes);
+    let accum_alloca = builder.build_alloca(accum_type, "alloca_walk_right_accum");
+    builder.build_store(accum_alloca, default);
+
+    let then_block = ctx.append_basic_block(parent, "then");
+    let cont_block = ctx.append_basic_block(parent, "branchcont");
+
+    let condition = builder.build_int_compare(
+        IntPredicate::UGT,
+        len,
+        ctx.i64_type().const_zero(),
+        "list_non_empty",
+    );
+
+    builder.build_conditional_branch(condition, then_block, cont_block);
+
+    builder.position_at_end(then_block);
+
+    match (func, func_layout) {
+        (BasicValueEnum::PointerValue(func_ptr), Layout::FunctionPointer(_, _)) => {
+            let elem_layout = match list_layout {
+                Layout::Builtin(Builtin::List(_, layout)) => layout,
+                _ => unreachable!("can only fold over a list"),
+            };
+
+            let elem_type = basic_type_from_layout(env.arena, ctx, elem_layout, env.ptr_bytes);
+            let elem_ptr_type = get_ptr_type(&elem_type, AddressSpace::Generic);
+
+            let list_ptr = load_list_ptr(builder, list_wrapper, elem_ptr_type);
+
+            let walk_right_loop = |_, elem: BasicValueEnum<'ctx>| {
+                // load current accumulator
+                let current = builder.build_load(accum_alloca, "retrieve_accum");
+
+                let call_site_value =
+                    builder.build_call(func_ptr, &[elem, current], "#walk_right_func");
+
+                // set the calling convention explicitly for this call
+                call_site_value.set_call_convention(crate::llvm::build::FAST_CALL_CONV);
+
+                let new_current = call_site_value
+                    .try_as_basic_value()
+                    .left()
+                    .unwrap_or_else(|| panic!("LLVM error: Invalid call by pointer."))
+                    .into_int_value();
+
+                builder.build_store(accum_alloca, new_current);
+            };
+
+            incrementing_elem_loop(
+                builder,
+                parent,
+                ctx,
+                LoopListArg { ptr: list_ptr, len },
+                "#index",
+                None,
+                walk_right_loop,
+            );
+        }
+
+        _ => {
+            unreachable!(
+                "Invalid function basic value enum or layout for List.keepIf : {:?}",
+                (func, func_layout)
+            );
+        }
+    }
+
+    builder.build_unconditional_branch(cont_block);
+
+    builder.position_at_end(cont_block);
+
+    builder.build_load(accum_alloca, "load_final_acum")
 }
 
 /// List.keepIf : List elem, (elem -> Bool) -> List elem
diff --git a/compiler/gen/tests/gen_list.rs b/compiler/gen/tests/gen_list.rs
index bf2d59f020..053b2fa8a7 100644
--- a/compiler/gen/tests/gen_list.rs
+++ b/compiler/gen/tests/gen_list.rs
@@ -119,7 +119,21 @@ mod gen_list {
         assert_evals_to!(
             indoc!(
                 r#"
-                List.walkRight [] (\a, b -> b) 0
+                List.walkRight [0x1] (\a, b -> a + b) 0
+                "#
+            ),
+            1,
+            i64
+        );
+
+        assert_evals_to!(
+            indoc!(
+                r#"
+                empty : List Int
+                empty =
+                    []
+
+                List.walkRight empty (\a, b -> a + b) 0
                 "#
             ),
             0,
diff --git a/compiler/mono/src/ir.rs b/compiler/mono/src/ir.rs
index 6afce9d633..803aac3269 100644
--- a/compiler/mono/src/ir.rs
+++ b/compiler/mono/src/ir.rs
@@ -3196,7 +3196,9 @@ fn call_by_name<'a>(
                             None => {
                                 // This must have been a runtime error.
                                 match procs.runtime_errors.get(&proc_name) {
-                                    Some(error) => Stmt::RuntimeError(error),
+                                    Some(error) => {
+                                        Stmt::RuntimeError(env.arena.alloc(format!("{:?}", error)))
+                                    }
                                     None => unreachable!("Proc name {:?} is invalid", proc_name),
                                 }
                             }
@@ -3205,10 +3207,10 @@ fn call_by_name<'a>(
                 }
             }
         }
-        Err(_) => {
+        Err(e) => {
             // This function code gens to a runtime error,
             // so attempting to call it will immediately crash.
-            Stmt::RuntimeError("")
+            Stmt::RuntimeError(env.arena.alloc(format!("{:?}", e)))
         }
     }
 }
diff --git a/compiler/solve/tests/solve_expr.rs b/compiler/solve/tests/solve_expr.rs
index 4a94d6e27f..6e70f7b09f 100644
--- a/compiler/solve/tests/solve_expr.rs
+++ b/compiler/solve/tests/solve_expr.rs
@@ -2717,4 +2717,32 @@ mod solve_expr {
             "{ x : Int, y ? Bool }* -> { x : Int, y : Bool }",
         );
     }
+
+    #[test]
+    fn list_walk_right() {
+        infer_eq_without_problem(
+            indoc!(
+                r#"
+                List.walkRight 
+                "#
+            ),
+            "List a, (a, b -> b), b -> b",
+        );
+    }
+
+    #[test]
+    fn list_walk_right_example() {
+        infer_eq_without_problem(
+            indoc!(
+                r#"
+                empty : List Int
+                empty = 
+                    []
+
+                List.walkRight empty (\a, b -> a + b) 0
+                "#
+            ),
+            "Int",
+        );
+    }
 }
diff --git a/compiler/solve/tests/solve_uniq_expr.rs b/compiler/solve/tests/solve_uniq_expr.rs
index 8539fca251..e0aba0ad85 100644
--- a/compiler/solve/tests/solve_uniq_expr.rs
+++ b/compiler/solve/tests/solve_uniq_expr.rs
@@ -2220,11 +2220,11 @@ mod solve_uniq_expr {
     }
 
     #[test]
-    fn list_foldr_sum() {
+    fn list_walkRight_sum() {
         infer_eq(
             indoc!(
                 r#"
-                    sum = \list -> List.foldr list Num.add 0
+                    sum = \list -> List.walkRight list Num.add 0
 
                     sum
                 "#
@@ -2291,9 +2291,9 @@ mod solve_uniq_expr {
     }
 
     #[test]
-    fn list_foldr() {
+    fn list_walkRight() {
         infer_eq(
-            "List.foldr",
+            "List.walkRight",
             "Attr * (Attr (* | b) (List (Attr b a)), Attr Shared (Attr b a, c -> c), c -> c)",
         );
     }
@@ -2313,11 +2313,11 @@ mod solve_uniq_expr {
     }
 
     #[test]
-    fn list_foldr_reverse() {
+    fn list_walkRight_reverse() {
         infer_eq(
             indoc!(
                 r#"
-                    reverse = \list -> List.foldr list (\e, l -> List.append l e) []
+                    reverse = \list -> List.walkRight list (\e, l -> List.append l e) []
 
                     reverse
                 "#
@@ -3115,4 +3115,32 @@ mod solve_uniq_expr {
             "Attr * (Attr (* | b | c) { x : Attr b (Num (Attr b a)), y ? Attr c (Num (Attr c a)) }* -> Attr d (Num (Attr d a)))"
         );
     }
+
+    #[test]
+    fn list_walk_right() {
+        infer_eq(
+            indoc!(
+                r#"
+                List.walkRight 
+                "#
+            ),
+            "Attr * (Attr (* | b) (List (Attr b a)), Attr Shared (Attr b a, c -> c), c -> c)",
+        );
+    }
+
+    #[test]
+    fn list_walk_right_example() {
+        infer_eq(
+            indoc!(
+                r#"
+                empty : List Int
+                empty = 
+                    []
+
+                List.walkRight empty (\a, b -> a + b) 0
+                "#
+            ),
+            "Attr a Int",
+        );
+    }
 }