diff --git a/bin/build b/bin/build
index f3f1a04..c912ecb 100755
--- a/bin/build
+++ b/bin/build
@@ -208,3 +208,7 @@ os.remove(config.hfsimg)
 if config.passthru is not None:
     wsheet = vol['MPW']['Worksheet'].data.decode('mac_roman').replace('\r', '\n')
     print(wsheet, end='')
+
+    # Slightly hacky way to extract an exit status
+    if re.search(r'^### MPW Shell - Execution of .* terminated', wsheet, re.MULTILINE):
+        sys.exit(1)