diff --git a/src/scripts/app.ts b/src/scripts/app.ts
index da803eb810..b8aba7a89c 100644
--- a/src/scripts/app.ts
+++ b/src/scripts/app.ts
@@ -273,6 +273,12 @@ export class ComfyApp {
       useExtensionService().invokeExtensions('onNodeOutputsUpdated', value)
   }
 
+  /**
+   * If the user has specified a preferred format to receive preview images in,
+   * this function will return that format as a url query param.
+   * If the node's outputs are not images, this param should not be used, as it will
+   * force the server to load the output file as an image.
+   */
   getPreviewFormatParam() {
     let preview_format = useSettingStore().get('Comfy.PreviewFormat')
     if (preview_format) return `&preview=${preview_format}`
diff --git a/src/stores/imagePreviewStore.ts b/src/stores/imagePreviewStore.ts
index ce95be3a77..83f5f8bcdd 100644
--- a/src/stores/imagePreviewStore.ts
+++ b/src/stores/imagePreviewStore.ts
@@ -3,6 +3,7 @@ import { defineStore } from 'pinia'
 
 import { ExecutedWsMessage, ResultItem } from '@/schemas/apiSchema'
 import { api } from '@/scripts/api'
+import { app } from '@/scripts/app'
 import { parseFilePath } from '@/utils/formatUtil'
 import { isVideoNode } from '@/utils/litegraphUtil'
 
@@ -17,11 +18,6 @@ const createOutputs = (
   }
 }
 
-const getPreviewParam = (node: LGraphNode): string => {
-  if (node.animatedImages || isVideoNode(node)) return ''
-  return app.getPreviewFormatParam()
-}
-
 export const useNodeOutputStore = defineStore('nodeOutput', () => {
   const getNodeId = (node: LGraphNode): string => node.id.toString()
 
@@ -35,6 +31,41 @@ export const useNodeOutputStore = defineStore('nodeOutput', () => {
     return app.nodePreviewImages[getNodeId(node)]
   }
 
+  /**
+   * Check if a node's outputs includes images that should/can be loaded normally
+   * by PIL.
+   */
+  const isImageOutputs = (
+    node: LGraphNode,
+    outputs: ExecutedWsMessage['output']
+  ): boolean => {
+    // If animated webp/png or video outputs, return false
+    if (node.animatedImages || isVideoNode(node)) return false
+
+    // If no images, return false
+    if (!outputs?.images?.length) return false
+
+    // If svg images, return false
+    if (outputs.images.some((image) => image.filename?.endsWith('svg')))
+      return false
+
+    return true
+  }
+
+  /**
+   * Get the preview param for the node's outputs.
+   *
+   * If the output is an image, use the user's preferred format (from settings).
+   * For non-image outputs, return an empty string, as including the preview param
+   * will force the server to load the output file as an image.
+   */
+  function getPreviewParam(
+    node: LGraphNode,
+    outputs: ExecutedWsMessage['output']
+  ): string {
+    return isImageOutputs(node, outputs) ? app.getPreviewFormatParam() : ''
+  }
+
   function getNodeImageUrls(node: LGraphNode): string[] | undefined {
     const previews = getNodePreviews(node)
     if (previews?.length) return previews
@@ -43,7 +74,7 @@ export const useNodeOutputStore = defineStore('nodeOutput', () => {
     if (!outputs?.images?.length) return
 
     const rand = app.getRandParam()
-    const previewParam = getPreviewParam(node)
+    const previewParam = getPreviewParam(node, outputs)
 
     return outputs.images.map((image) => {
       const imgUrlPart = new URLSearchParams(image)
@@ -78,6 +109,7 @@ export const useNodeOutputStore = defineStore('nodeOutput', () => {
     getNodeOutputs,
     getNodeImageUrls,
     getNodePreviews,
-    setNodeOutputs
+    setNodeOutputs,
+    getPreviewParam
   }
 })
diff --git a/tests-ui/tests/store/imagePreviewStore.test.ts b/tests-ui/tests/store/imagePreviewStore.test.ts
new file mode 100644
index 0000000000..0a464ba815
--- /dev/null
+++ b/tests-ui/tests/store/imagePreviewStore.test.ts
@@ -0,0 +1,98 @@
+import { LGraphNode } from '@comfyorg/litegraph'
+import { createPinia, setActivePinia } from 'pinia'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { ExecutedWsMessage } from '@/schemas/apiSchema'
+import { app } from '@/scripts/app'
+import { useNodeOutputStore } from '@/stores/imagePreviewStore'
+import * as litegraphUtil from '@/utils/litegraphUtil'
+
+vi.mock('@/utils/litegraphUtil', () => ({
+  isVideoNode: vi.fn()
+}))
+
+vi.mock('@/scripts/app', () => ({
+  app: {
+    getPreviewFormatParam: vi.fn(() => '&format=test_webp')
+  }
+}))
+
+const createMockNode = (overrides: Partial<LGraphNode> = {}): LGraphNode =>
+  ({
+    id: 1,
+    type: 'TestNode',
+    ...overrides
+  }) as LGraphNode
+
+const createMockOutputs = (
+  images?: ExecutedWsMessage['output']['images']
+): ExecutedWsMessage['output'] => ({ images })
+
+describe('imagePreviewStore getPreviewParam', () => {
+  beforeEach(() => {
+    setActivePinia(createPinia())
+    vi.clearAllMocks()
+    vi.mocked(litegraphUtil.isVideoNode).mockReturnValue(false)
+  })
+
+  it('should return empty string if node.animatedImages is true', () => {
+    const store = useNodeOutputStore()
+    // @ts-expect-error `animatedImages` property is not typed
+    const node = createMockNode({ animatedImages: true })
+    const outputs = createMockOutputs([{ filename: 'img.png' }])
+    expect(store.getPreviewParam(node, outputs)).toBe('')
+    expect(vi.mocked(app).getPreviewFormatParam).not.toHaveBeenCalled()
+  })
+
+  it('should return empty string if isVideoNode returns true', () => {
+    const store = useNodeOutputStore()
+    vi.mocked(litegraphUtil.isVideoNode).mockReturnValue(true)
+    const node = createMockNode()
+    const outputs = createMockOutputs([{ filename: 'img.png' }])
+    expect(store.getPreviewParam(node, outputs)).toBe('')
+    expect(vi.mocked(app).getPreviewFormatParam).not.toHaveBeenCalled()
+  })
+
+  it('should return empty string if outputs.images is undefined', () => {
+    const store = useNodeOutputStore()
+    const node = createMockNode()
+    const outputs: ExecutedWsMessage['output'] = {}
+    expect(store.getPreviewParam(node, outputs)).toBe('')
+    expect(vi.mocked(app).getPreviewFormatParam).not.toHaveBeenCalled()
+  })
+
+  it('should return empty string if outputs.images is empty', () => {
+    const store = useNodeOutputStore()
+    const node = createMockNode()
+    const outputs = createMockOutputs([])
+    expect(store.getPreviewParam(node, outputs)).toBe('')
+    expect(vi.mocked(app).getPreviewFormatParam).not.toHaveBeenCalled()
+  })
+
+  it('should return empty string if outputs.images contains SVG images', () => {
+    const store = useNodeOutputStore()
+    const node = createMockNode()
+    const outputs = createMockOutputs([{ filename: 'img.svg' }])
+    expect(store.getPreviewParam(node, outputs)).toBe('')
+    expect(vi.mocked(app).getPreviewFormatParam).not.toHaveBeenCalled()
+  })
+
+  it('should return format param for standard image outputs', () => {
+    const store = useNodeOutputStore()
+    const node = createMockNode()
+    const outputs = createMockOutputs([{ filename: 'img.png' }])
+    expect(store.getPreviewParam(node, outputs)).toBe('&format=test_webp')
+    expect(vi.mocked(app).getPreviewFormatParam).toHaveBeenCalledTimes(1)
+  })
+
+  it('should return format param for multiple standard images', () => {
+    const store = useNodeOutputStore()
+    const node = createMockNode()
+    const outputs = createMockOutputs([
+      { filename: 'img1.png' },
+      { filename: 'img2.jpg' }
+    ])
+    expect(store.getPreviewParam(node, outputs)).toBe('&format=test_webp')
+    expect(vi.mocked(app).getPreviewFormatParam).toHaveBeenCalledTimes(1)
+  })
+})