diff --git a/CHANGELOG.md b/CHANGELOG.md
index 605608182c..aa9c0bc6ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,7 @@ Thank you to all who have contributed!
 
 ### Fixed
 - Return type of `partiql-ast`'s `SqlDialect` for `defaultReturn` to be a `SqlBlock` rather than `Nothing`
+- Flatten `CASE WHEN` branch type in `PlanTyper`
 
 ### Removed
 
diff --git a/partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/PlanTyper.kt b/partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/PlanTyper.kt
index 1c15078553..42fd0b9485 100644
--- a/partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/PlanTyper.kt
+++ b/partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/PlanTyper.kt
@@ -796,7 +796,7 @@ internal class PlanTyper(
                     }
 
                     // Replace the result's type
-                    val type = AnyOfType(ref.type.allTypes.filterIsInstance<StructType>().toSet())
+                    val type = AnyOfType(ref.type.allTypes.filterIsInstance<StructType>().toSet()).flatten()
                     val replacementVal = ref.copy(type = type)
                     val rex = when (ref.op is Rex.Op.Var.Resolved) {
                         true -> RexReplacer.replace(result, ref, replacementVal)