diff --git a/compiler/builtins/src/std.rs b/compiler/builtins/src/std.rs
index 5d054ad831..dab48890e3 100644
--- a/compiler/builtins/src/std.rs
+++ b/compiler/builtins/src/std.rs
@@ -1381,6 +1381,13 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         Box::new(bool_type()),
     );
 
+    // isErr : Result * * -> bool
+    add_top_level_function_type!(
+        Symbol::RESULT_IS_ERR,
+        vec![result_type(flex(TVAR1), flex(TVAR3))],
+        Box::new(bool_type()),
+    );
+
     types
 }
 
diff --git a/compiler/can/src/builtins.rs b/compiler/can/src/builtins.rs
index ddabf11685..c718f22b5f 100644
--- a/compiler/can/src/builtins.rs
+++ b/compiler/can/src/builtins.rs
@@ -193,6 +193,7 @@ pub fn builtin_defs_map(symbol: Symbol, var_store: &mut VarStore) -> Option<Def>
         RESULT_AFTER => result_after,
         RESULT_WITH_DEFAULT => result_with_default,
         RESULT_IS_OK => result_is_ok,
+        RESULT_IS_ERR => result_is_err,
     }
 }
 
@@ -3992,6 +3993,83 @@ fn result_with_default(symbol: Symbol, var_store: &mut VarStore) -> Def {
     )
 }
 
+fn result_is_err(symbol: Symbol, var_store: &mut VarStore) -> Def {
+    let ret_var = var_store.fresh();
+    let result_var = var_store.fresh();
+
+    let mut branches = vec![];
+
+    {
+        // ok branch
+        let tag_name = TagName::Global("Ok".into());
+
+        let pattern = Pattern::AppliedTag {
+            whole_var: result_var,
+            ext_var: var_store.fresh(),
+            tag_name,
+            arguments: vec![(var_store.fresh(), no_region(Pattern::Underscore))],
+        };
+
+        let false_expr = Tag {
+            variant_var: var_store.fresh(),
+            ext_var: var_store.fresh(),
+            name: TagName::Global("False".into()),
+            arguments: vec![],
+        };
+
+        let branch = WhenBranch {
+            patterns: vec![no_region(pattern)],
+            value: no_region(false_expr),
+            guard: None,
+        };
+
+        branches.push(branch);
+    }
+
+    {
+        // err branch
+        let tag_name = TagName::Global("Err".into());
+
+        let pattern = Pattern::AppliedTag {
+            whole_var: result_var,
+            ext_var: var_store.fresh(),
+            tag_name,
+            arguments: vec![(var_store.fresh(), no_region(Pattern::Underscore))],
+        };
+
+        let true_expr = Tag {
+            variant_var: var_store.fresh(),
+            ext_var: var_store.fresh(),
+            name: TagName::Global("True".into()),
+            arguments: vec![],
+        };
+
+        let branch = WhenBranch {
+            patterns: vec![no_region(pattern)],
+            value: no_region(true_expr),
+            guard: None,
+        };
+
+        branches.push(branch);
+    }
+
+    let body = When {
+        cond_var: result_var,
+        expr_var: ret_var,
+        region: Region::zero(),
+        loc_cond: Box::new(no_region(Var(Symbol::ARG_1))),
+        branches,
+    };
+
+    defn(
+        symbol,
+        vec![(result_var, Symbol::ARG_1)],
+        var_store,
+        body,
+        ret_var,
+    )
+}
+
 fn result_is_ok(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let ret_var = var_store.fresh();
     let result_var = var_store.fresh();
diff --git a/compiler/module/src/symbol.rs b/compiler/module/src/symbol.rs
index 92345fbdf0..2233003ca0 100644
--- a/compiler/module/src/symbol.rs
+++ b/compiler/module/src/symbol.rs
@@ -1079,6 +1079,7 @@ define_builtins! {
         3 RESULT_WITH_DEFAULT: "withDefault"
         4 RESULT_AFTER: "after"
         5 RESULT_IS_OK: "isOk"
+        6 RESULT_IS_ERR: "isErr"
     }
     6 DICT: "Dict" => {
         0 DICT_DICT: "Dict" imported // the Dict.Dict type alias
diff --git a/compiler/test_gen/src/gen_result.rs b/compiler/test_gen/src/gen_result.rs
index bfb0634326..4b86af9e83 100644
--- a/compiler/test_gen/src/gen_result.rs
+++ b/compiler/test_gen/src/gen_result.rs
@@ -189,3 +189,33 @@ fn is_ok() {
         bool
     );
 }
+
+#[test]
+#[cfg(any(feature = "gen-llvm"))]
+fn is_err() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            result : Result I64 {}
+            result = Ok 2
+
+            Result.isErr result
+            "#
+        ),
+        false,
+        bool
+    );
+
+    assert_evals_to!(
+        indoc!(
+            r#"
+            result : Result I64 {}
+            result = Err {}
+
+            Result.isErr result
+            "#
+        ),
+        true,
+        bool
+    );
+}