diff --git a/builtins/Float.roc b/builtins/Float.roc
index 1761ecb347..10309e6a08 100644
--- a/builtins/Float.roc
+++ b/builtins/Float.roc
@@ -69,7 +69,7 @@ interface Float
 
 #round : Float -> Int
 round = \num ->
-    case num is
+    when num is
         0.0 -> 0
         _ -> 1
 
@@ -110,7 +110,7 @@ round = \num ->
 ## >>>     |> Float.div 2.0
 #div : Float, Float -> Result Float DivByZero
 div = \numerator, denominator ->
-    case numerator is
+    when numerator is
         0.0 -> 0.0 # TODO return Result!
         _ -> denominator
 
diff --git a/src/fmt/expr.rs b/src/fmt/expr.rs
index 526f35c3b3..27b492f72d 100644
--- a/src/fmt/expr.rs
+++ b/src/fmt/expr.rs
@@ -134,7 +134,7 @@ pub fn fmt_expr<'a>(
         }
         Case(loc_condition, branches) => {
             buf.push_str("\
-            case ");
+            when ");
             fmt_expr(buf, &loc_condition.value, indent, false, true);
             buf.push_str(" is\n");
 
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index 21aef45c2b..65fa21bff6 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -1139,7 +1139,7 @@ pub fn colon_with_indent<'a>() -> impl Parser<'a, u16> {
 
 pub fn case_with_indent<'a>() -> impl Parser<'a, u16> {
     move |arena, state: State<'a>| {
-        string(keyword::CASE)
+        string(keyword::WHEN)
             .parse(arena, state)
             .map(|((), state)| (state.indent_col, state))
     }
diff --git a/tests/test_canonicalize.rs b/tests/test_canonicalize.rs
index 0e60687216..fea07b2f85 100644
--- a/tests/test_canonicalize.rs
+++ b/tests/test_canonicalize.rs
@@ -249,17 +249,17 @@ mod test_canonicalize {
             let src = indoc!(
                 r#"
             g = \x ->
-                case x is
+                when x is
                     0 -> 0
                     _ -> g (x - 1)
 
             h = \x ->
-                case x is
+                when x is
                     0 -> 0
                     _ -> g (x - 1)
 
             p = \x ->
-                case x is
+                when x is
                     0 -> 0
                     1 -> g (x - 1)
                     _ -> p (x - 1)
@@ -288,7 +288,7 @@ mod test_canonicalize {
             let src = indoc!(
                 r#"
                 g = \x ->
-                    case x is
+                    when x is
                         0 -> 0
                         _ -> g (x + 1)
 
@@ -327,7 +327,7 @@ mod test_canonicalize {
         let src = indoc!(
             r#"
             q = \x ->
-                    case q x is
+                    when q x is
                         _ -> 0
 
             0
@@ -348,12 +348,12 @@ mod test_canonicalize {
             let src = indoc!(
                 r#"
             q = \x ->
-                    case x is
+                    when x is
                         0 -> 0
                         _ -> p (x - 1)
 
             p = \x ->
-                    case x is
+                    when x is
                         0 -> 0
                         _ -> q (x - 1)
 
diff --git a/tests/test_eval.rs b/tests/test_eval.rs
index 752d9e791c..d72a372364 100644
--- a/tests/test_eval.rs
+++ b/tests/test_eval.rs
@@ -87,7 +87,7 @@ mod test_gen {
         assert_evals_to!(
             indoc!(
                 r#"
-            case 1 is
+            when 1 is
                 1 -> 12
                 _ -> 34
             "#
@@ -102,7 +102,7 @@ mod test_gen {
         assert_evals_to!(
             indoc!(
                 r#"
-            case 2 is
+            when 2 is
                 1 -> 63
                 _ -> 48
             "#
diff --git a/tests/test_format.rs b/tests/test_format.rs
index 29a89cd7ca..1f44ae5184 100644
--- a/tests/test_format.rs
+++ b/tests/test_format.rs
@@ -695,7 +695,7 @@ mod test_format {
     fn integer_case() {
         expr_formats_same(indoc!(
             r#"
-            case b is
+            when b is
                 1 ->
                     1
 
@@ -710,7 +710,7 @@ mod test_format {
         expr_formats_to(
             indoc!(
                 r#"
-            case year is
+            when year is
                 1999 ->
 
 
@@ -725,7 +725,7 @@ mod test_format {
             ),
             indoc!(
                 r#"
-            case year is
+            when year is
                 1999 ->
                     1
 
@@ -740,10 +740,10 @@ mod test_format {
     fn case_with_comments() {
         expr_formats_same(indoc!(
             r#"
-            case b is
+            when b is
                 # look at cases
                 1 ->
-                    # case 1
+                    # when 1
                     1
 
                 # important
@@ -761,9 +761,9 @@ mod test_format {
     fn nested_case() {
         expr_formats_same(indoc!(
             r#"
-            case b is
+            when b is
                 _ ->
-                    case c is
+                    when c is
                         _ ->
                             1
         "#
@@ -775,9 +775,9 @@ mod test_format {
         expr_formats_to(
             indoc!(
                 r#"
-            case b is
+            when b is
                 1 ->
-                    1 # case 1
+                    1 # when 1
 
                 # fall through
                 _ ->
@@ -786,11 +786,11 @@ mod test_format {
             ),
             indoc!(
                 r#"
-            case b is
+            when b is
                 1 ->
                     1
 
-                # case 1
+                # when 1
                 # fall through
                 _ ->
                     2
diff --git a/tests/test_infer.rs b/tests/test_infer.rs
index 43220c57e9..31a2c21bdd 100644
--- a/tests/test_infer.rs
+++ b/tests/test_infer.rs
@@ -833,7 +833,7 @@ mod test_infer {
         infer_eq(
             indoc!(
                 r#"
-                case 1 is
+                when 1 is
                  1 -> 2
                  3 -> 4
             "#
diff --git a/tests/test_parse.rs b/tests/test_parse.rs
index 4e67a7e037..d95df07c23 100644
--- a/tests/test_parse.rs
+++ b/tests/test_parse.rs
@@ -1322,7 +1322,7 @@ mod test_parse {
             &arena,
             indoc!(
                 r#"
-                case x is
+                when x is
                  "blah" -> 1
                  "mise" -> 2
                 "#
@@ -1356,7 +1356,7 @@ mod test_parse {
             &arena,
             indoc!(
                 r#"
-                case x is
+                when x is
                  1 -> 2
                  3 -> 4
                 "#
@@ -1396,7 +1396,7 @@ mod test_parse {
             &arena,
             indoc!(
                 r#"
-                case x is
+                when x is
                  { y } -> 2
                  { z, w } -> 4
                 "#
diff --git a/tests/test_uniqueness_infer.rs b/tests/test_uniqueness_infer.rs
index 826c4b3f33..25a50cfa73 100644
--- a/tests/test_uniqueness_infer.rs
+++ b/tests/test_uniqueness_infer.rs
@@ -863,7 +863,7 @@ mod test_infer_uniq {
         infer_eq(
             indoc!(
                 r#"
-                case 1 is
+                when 1 is
                  1 -> 2
                  3 -> 4
             "#