diff --git a/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/TreehouseAppContent.kt b/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/TreehouseAppContent.kt
index 0e509b8cf9..c2d082c712 100644
--- a/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/TreehouseAppContent.kt
+++ b/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/TreehouseAppContent.kt
@@ -49,7 +49,7 @@ private class State<A : AppService>(
 private sealed interface ViewState {
   object None : ViewState
 
-  class Preloading(
+  data class Preloading(
     val onBackPressedDispatcher: OnBackPressedDispatcher,
     val uiConfiguration: UiConfiguration,
   ) : ViewState
@@ -87,6 +87,7 @@ internal class TreehouseAppContent<A : AppService>(
     dispatchers.checkUi()
     val previousState = stateFlow.value
 
+    if (previousState.viewState == ViewState.Preloading(onBackPressedDispatcher, uiConfiguration)) return // Idempotent.
     check(previousState.viewState is ViewState.None)
 
     val nextViewState = ViewState.Preloading(onBackPressedDispatcher, uiConfiguration)
diff --git a/redwood-treehouse-host/src/commonTest/kotlin/app/cash/redwood/treehouse/TreehouseAppContentTest.kt b/redwood-treehouse-host/src/commonTest/kotlin/app/cash/redwood/treehouse/TreehouseAppContentTest.kt
index fcc5dd098b..3c6f0e7b0c 100644
--- a/redwood-treehouse-host/src/commonTest/kotlin/app/cash/redwood/treehouse/TreehouseAppContentTest.kt
+++ b/redwood-treehouse-host/src/commonTest/kotlin/app/cash/redwood/treehouse/TreehouseAppContentTest.kt
@@ -446,6 +446,23 @@ class TreehouseAppContentTest {
     content.unbind()
   }
 
+  @Test
+  fun preload_idempotent() = runTest {
+    val content = treehouseAppContent()
+
+    codeHost.startCodeSession("codeSessionA")
+    eventLog.takeEvent("codeSessionA.start()")
+
+    content.preload(onBackPressedDispatcher, uiConfiguration)
+    eventLog.takeEvent("codeSessionA.app.uis[0].start()")
+
+    content.preload(onBackPressedDispatcher, uiConfiguration)
+    eventLog.assertNoEvents()
+
+    content.unbind()
+    eventLog.takeEvent("codeSessionA.app.uis[0].close()")
+  }
+
   @Test
   fun bind_idempotent() = runTest {
     val content = treehouseAppContent()