diff --git a/src/stores/subgraphStore.test.ts b/src/stores/subgraphStore.test.ts
index db322a8b0a4..a25ac9bc720 100644
--- a/src/stores/subgraphStore.test.ts
+++ b/src/stores/subgraphStore.test.ts
@@ -285,6 +285,26 @@ describe('useSubgraphStore', () => {
     consoleSpy.mockRestore()
   })
 
+  it('should reject blueprints without a root node', async () => {
+    const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
+    await mockFetch({
+      'empty-node.json': {
+        ...mockGraph,
+        nodes: []
+      }
+    })
+
+    const error = consoleSpy.mock.calls.find(
+      ([message]) => message === 'Failed to load subgraph blueprint'
+    )?.[1]
+    expect(error).toBeInstanceOf(TypeError)
+    expect((error as Error).message).toBe(
+      "Subgraph blueprint 'empty-node' must contain a root node"
+    )
+    expect(store.subgraphBlueprints).toHaveLength(0)
+    consoleSpy.mockRestore()
+  })
+
   it('should handle global blueprint with rejected data promise gracefully', async () => {
     const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
     await mockFetch(
diff --git a/src/stores/subgraphStore.ts b/src/stores/subgraphStore.ts
index 99fe96ef63b..b394b8cfacb 100644
--- a/src/stores/subgraphStore.ts
+++ b/src/stores/subgraphStore.ts
@@ -39,6 +39,10 @@ async function confirmOverwrite(name: string): Promise<boolean | null> {
   })
 }
 
+type ValidSubgraphWorkflowJSON = ComfyWorkflowJSON & {
+  definitions: NonNullable<ComfyWorkflowJSON['definitions']>
+}
+
 export const useSubgraphStore = defineStore('subgraph', () => {
   class SubgraphBlueprint extends ComfyWorkflow {
     static override readonly basePath = 'subgraphs/'
@@ -54,18 +58,20 @@ export const useSubgraphStore = defineStore('subgraph', () => {
       this.hasPromptedSave = !confirmFirstSave
     }
 
-    validateSubgraph() {
-      if (!this.activeState?.definitions)
+    validateSubgraph(): ValidSubgraphWorkflowJSON {
+      const activeState = this.activeState
+      if (!activeState?.definitions)
         throw new Error(
           'The root graph of a subgraph blueprint must consist of only a single subgraph node'
         )
-      const { subgraphs } = this.activeState.definitions
-      const { nodes } = this.activeState
+      const validState = activeState as ValidSubgraphWorkflowJSON
+      const { subgraphs } = validState.definitions
+      const { nodes } = validState
       //Instanceof doesn't function as nodes are serialized
       function isSubgraphNode(node: ComfyNode) {
         return node && subgraphs.some((s) => s.id === node.type)
       }
-      if (nodes.length == 1 && isSubgraphNode(nodes[0])) return
+      if (nodes.length == 1 && isSubgraphNode(nodes[0])) return validState
       const errors: Record<SerializedNodeId, NodeError> = {}
       //mark errors for all but first subgraph node
       let firstSubgraphFound = false
@@ -88,7 +94,7 @@ export const useSubgraphStore = defineStore('subgraph', () => {
     }
 
     override async save(): Promise<UserFile> {
-      this.validateSubgraph()
+      const activeState = this.validateSubgraph()
       if (
         !this.hasPromptedSave &&
         useSettingStore().get('Comfy.Workflow.WarnBlueprintOverwrite')
@@ -97,7 +103,7 @@ export const useSubgraphStore = defineStore('subgraph', () => {
         this.hasPromptedSave = true
       }
       // Extract metadata from subgraph.extra to workflow.extra before saving
-      this.extractMetadataToWorkflowExtra()
+      this.extractMetadataToWorkflowExtra(activeState)
       const ret = await super.save()
       // Force reload to update initialState with saved metadata
       registerNodeDef(await this.load({ force: true }), {
@@ -110,13 +116,14 @@ export const useSubgraphStore = defineStore('subgraph', () => {
      * Moves all properties (except workflowRendererVersion) from subgraph.extra
      * to workflow.extra, then removes from subgraph.extra to avoid duplication.
      */
-    private extractMetadataToWorkflowExtra(): void {
-      if (!this.activeState) return
-      const subgraph = this.activeState.definitions?.subgraphs?.[0]
+    private extractMetadataToWorkflowExtra(
+      activeState: ValidSubgraphWorkflowJSON
+    ): void {
+      const subgraph = activeState.definitions.subgraphs?.[0]
       if (!subgraph?.extra) return
 
       const sgExtra = subgraph.extra as Record<string, unknown>
-      const workflowExtra = (this.activeState.extra ??= {}) as Record<
+      const workflowExtra = (activeState.extra ??= {}) as Record<
         string,
         unknown
       >
@@ -129,10 +136,10 @@ export const useSubgraphStore = defineStore('subgraph', () => {
     }
 
     override async saveAs(path: string) {
-      this.validateSubgraph()
+      const activeState = this.validateSubgraph()
       this.hasPromptedSave = true
       // Extract metadata from subgraph.extra to workflow.extra before saving
-      this.extractMetadataToWorkflowExtra()
+      this.extractMetadataToWorkflowExtra(activeState)
       const ret = await super.saveAs(path)
       // Force reload to update initialState with saved metadata
       registerNodeDef(await this.load({ force: true }), {
@@ -146,14 +153,20 @@ export const useSubgraphStore = defineStore('subgraph', () => {
       if (!force && this.isLoaded) return await super.load({ force })
       const loaded = await super.load({ force })
       const st = loaded.activeState
+      const rootNode = st.nodes[0]
+      if (!rootNode) {
+        throw new TypeError(
+          `Subgraph blueprint '${this.filename}' must contain a root node`
+        )
+      }
       const sg = (st.definitions?.subgraphs ?? []).find(
-        (sg) => sg.id == st.nodes[0].type
+        (sg) => sg.id == rootNode.type
       )
       if (!sg)
         throw new Error(
           'Loaded subgraph blueprint does not contain valid subgraph'
         )
-      sg.name = st.nodes[0].title = this.filename
+      sg.name = rootNode.title = this.filename
 
       // Copy blueprint metadata from workflow extra to subgraph extra
       // so it's available when editing via canvas.subgraph.extra
@@ -277,7 +290,11 @@ export const useSubgraphStore = defineStore('subgraph', () => {
     name: string = workflow.filename
   ) {
     const subgraphNode = workflow.changeTracker.initialState.nodes[0]
-    if (!subgraphNode) throw new Error('Invalid Subgraph Blueprint')
+    if (!subgraphNode) {
+      throw new TypeError(
+        `Subgraph blueprint '${name}' must contain a root node`
+      )
+    }
     subgraphNode.inputs ??= []
     subgraphNode.outputs ??= []
     //NOTE: Types are cast to string. This is only used for input coloring on previews