diff --git a/knots/parallelism.scm b/knots/parallelism.scm
index 41ae676..fc3d039 100644
--- a/knots/parallelism.scm
+++ b/knots/parallelism.scm
@@ -238,8 +238,7 @@
                        #f))))
               channels-to-results))))))))
 
-(define* (fiberize proc #:key (parallelism 1)
-                   (show-backtrace? (const #t)))
+(define* (fiberize proc #:key (parallelism 1))
   (let ((channel (make-channel)))
     (for-each
      (lambda _