diff --git a/source/session.ts b/source/session.ts
index ca06f57..b2e98b7 100644
--- a/source/session.ts
+++ b/source/session.ts
@@ -1090,7 +1090,7 @@ export class Session<
         },
       });
 
-      uploader.start();
+      uploader.start().catch(reject);
     });
   }
 }
diff --git a/source/uploader.ts b/source/uploader.ts
index 2e16c42..cea1f81 100644
--- a/source/uploader.ts
+++ b/source/uploader.ts
@@ -177,7 +177,14 @@ export class Uploader<TEntityTypeMap extends Record<string, any>> {
   /** Initiate upload. Promise is resolved once preflight is complete and upload started. */
   async start() {
     logger.debug("Upload starting", this.componentId);
-    await this.uploadPreflight();
+    try {
+      await this.uploadPreflight();
+    } catch (error) {
+      if (this.onError) {
+        this.onError(error as Error);
+      }
+      throw error;
+    }
     if (!this.uploadMetadata) {
       throw new Error("Failed to get upload metadata");
     }