diff --git a/frontend/src/lib/components/ModulePreviewForm.svelte b/frontend/src/lib/components/ModulePreviewForm.svelte
index 3de3d199d8..527c019950 100644
--- a/frontend/src/lib/components/ModulePreviewForm.svelte
+++ b/frontend/src/lib/components/ModulePreviewForm.svelte
@@ -1,7 +1,7 @@
 <script lang="ts">
 	import type { Schema } from '$lib/common'
 
-	import { allTrue } from '$lib/utils'
+	import { allTrue, sendUserToast } from '$lib/utils'
 	import { RefreshCw } from 'lucide-svelte'
 	import ArgInput from './ArgInput.svelte'
 	import { Button } from './common'
@@ -101,8 +101,11 @@
 	let args = $state(<Record<string, any>>{})
 
 	onMount(() => {
+		if (!testSteps) {
+			sendUserToast('testSteps module not initialized. Preview will not work.', true)
+		}
 		testSteps?.updateStepArgs(mod.id, flowStateStore.val, flowStore?.val, previewArgs?.val)
-		args = testSteps?.getStepArgs(mod.id) ?? { value: {} }
+		args = testSteps?.getStepArgs(mod.id)
 	})
 </script>
 
diff --git a/frontend/src/lib/components/flows/testSteps.svelte.ts b/frontend/src/lib/components/flows/testSteps.svelte.ts
index 600b4fe6e2..7d66bb340f 100644
--- a/frontend/src/lib/components/flows/testSteps.svelte.ts
+++ b/frontend/src/lib/components/flows/testSteps.svelte.ts
@@ -21,7 +21,11 @@ export class TestSteps {
 		this.#steps[moduleId].value = args
 	}
 
-	getStepArgs(moduleId: string): ModuleArgs | undefined {
+	getStepArgs(moduleId: string): ModuleArgs {
+		let args = this.#steps[moduleId]
+		if (!args) {
+			this.#steps[moduleId] = { value: {} }
+		}
 		return this.#steps[moduleId]
 	}
 
@@ -143,10 +147,6 @@ export class TestSteps {
 		flow: OpenFlow | undefined,
 		previewArgs: Record<string, any> | undefined
 	) {
-		if (id == 'preprocessor') {
-			this.#steps[id] = { value: {} }
-			return
-		}
 		if (!flowState || !flow) {
 			return
 		}