diff --git a/crates/compiler/solve/src/solve.rs b/crates/compiler/solve/src/solve.rs
index 89097cf9d2..c0bd6eb27d 100644
--- a/crates/compiler/solve/src/solve.rs
+++ b/crates/compiler/solve/src/solve.rs
@@ -1847,6 +1847,11 @@ fn open_tag_union(subs: &mut Subs, var: Variable) {
                 stack.extend(subs.get_subs_slice(fields.variables()));
             }
 
+            Structure(Tuple(elems, _)) => {
+                // Open up all nested tag unions.
+                stack.extend(subs.get_subs_slice(elems.variables()));
+            }
+
             Structure(Apply(Symbol::LIST_LIST, args)) => {
                 // Open up nested tag unions.
                 stack.extend(subs.get_subs_slice(args));
diff --git a/crates/reporting/tests/test_reporting.rs b/crates/reporting/tests/test_reporting.rs
index a50debc07c..06c770f122 100644
--- a/crates/reporting/tests/test_reporting.rs
+++ b/crates/reporting/tests/test_reporting.rs
@@ -13170,4 +13170,17 @@ I recommend using camelCase. It's the standard style in Roc code!
     I would have to crash if I saw one of those! Add branches for them!
     "###
     );
+
+    test_no_problem!(
+        openness_constraint_opens_under_tuple,
+        indoc!(
+            r#"
+              x : [A, B, C]
+              when (x, 1u8) is
+                (A, _) -> Bool.true
+                (B, _) -> Bool.true
+                _ -> Bool.true
+            "#
+        )
+    );
 }