diff --git a/backend/src/workspaces/preprocessing-state.ts b/backend/src/workspaces/preprocessing-state.ts
index 95ee6cd3..d7d52f13 100644
--- a/backend/src/workspaces/preprocessing-state.ts
+++ b/backend/src/workspaces/preprocessing-state.ts
@@ -282,7 +282,13 @@ export class PreprocessingStateStore {
     } catch (error) {
       if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
         if (error instanceof PreprocessingStateError) throw error;
-        if (options.runId) throw error;
+        throw error;
+      }
+      if (options.runId) {
+        throw new PreprocessingStateError(
+          "preprocessing_resume_mismatch",
+          "Workspace preprocessing run is unavailable",
+        );
       }
     }
     const job: PreprocessingJobState = {