diff --git a/crates/compiler/parse/src/expr.rs b/crates/compiler/parse/src/expr.rs
index 757af05a69..ff6d8e83d2 100644
--- a/crates/compiler/parse/src/expr.rs
+++ b/crates/compiler/parse/src/expr.rs
@@ -346,6 +346,7 @@ fn parse_expr_start<'a>(
         loc!(move |a, s, m| parse_expr_operator_chain(m, options, a, s)),
         fail_expr_start_e()
     ]
+    .trace("expr_start")
     .parse(arena, state, min_indent)
 }
 
@@ -2076,10 +2077,10 @@ mod when {
                     parser::keyword_e(keyword::IS, EWhen::Is)
                 )
             ),
-            move |arena, state, progress, (case_indent, loc_condition), min_indent| {
+            move |arena, state, _progress, (case_indent, loc_condition), min_indent| {
                 if case_indent < min_indent {
                     return Err((
-                        progress,
+                        MadeProgress,
                         // TODO maybe pass case_indent here?
                         EWhen::PatternAlignment(5, state.pos()),
                         state,
@@ -2089,15 +2090,18 @@ mod when {
                 // Everything in the branches must be indented at least as much as the case itself.
                 let min_indent = case_indent;
 
-                let (p1, branches, state) = branches(options).parse(arena, state, min_indent)?;
+                let (_p1, branches, state) = branches(options)
+                    .parse(arena, state, min_indent)
+                    .map_err(|(_p, e, s)| (MadeProgress, e, s))?;
 
                 Ok((
-                    progress.or(p1),
+                    MadeProgress,
                     Expr::When(arena.alloc(loc_condition), branches.into_bump_slice()),
                     state,
                 ))
             },
         )
+        .trace("when")
     }
 
     /// Parsing when with indentation.
diff --git a/crates/compiler/parse/src/parser.rs b/crates/compiler/parse/src/parser.rs
index d190afd086..328d4b3b0a 100644
--- a/crates/compiler/parse/src/parser.rs
+++ b/crates/compiler/parse/src/parser.rs
@@ -1380,11 +1380,12 @@ macro_rules! and {
 macro_rules! one_of {
     ($p1:expr, $p2:expr) => {
         move |arena: &'a bumpalo::Bump, state: $crate::state::State<'a>, min_indent: u32| {
+            let original_state = state.clone();
 
             match $p1.parse(arena, state, min_indent) {
                 valid @ Ok(_) => valid,
                 Err((MadeProgress, fail, state)) => Err((MadeProgress, fail, state)),
-                Err((NoProgress, _, state)) => $p2.parse(arena, state, min_indent),
+                Err((NoProgress, _, _)) => $p2.parse(arena, original_state, min_indent),
             }
         }
     };
diff --git a/crates/reporting/tests/test_reporting.rs b/crates/reporting/tests/test_reporting.rs
index ccd134d44b..dd7e4d5953 100644
--- a/crates/reporting/tests/test_reporting.rs
+++ b/crates/reporting/tests/test_reporting.rs
@@ -4837,14 +4837,27 @@ mod test_reporting {
             "#
         ),
         @r###"
-    ── MISSING EXPRESSION ───────────────────── tmp/pattern_binds_keyword/Test.roc ─
+    ── MISSING ARROW ────────────────────────── tmp/pattern_binds_keyword/Test.roc ─
 
-    I am partway through parsing a `when` expression, but I got stuck here:
+    I am partway through parsing a `when` expression, but got stuck here:
 
     5│          Just when ->
-                           ^
+                     ^
 
-    I was expecting to see an expression like 42 or "hello".
+    I was expecting to see an arrow next.
+
+    Note: Sometimes I get confused by indentation, so try to make your `when`
+    look something like this:
+
+        when List.first plants is
+          Ok n ->
+            n
+
+          Err _ ->
+            200
+
+    Notice the indentation. All patterns are aligned, and each branch is
+    indented a bit more than the corresponding pattern. That is important!
     "###
     );