diff --git a/lang/ninja/src/build.sld b/lang/ninja/src/build.sld
index 397895d..b1f7c79 100644
--- a/lang/ninja/src/build.sld
+++ b/lang/ninja/src/build.sld
@@ -2,6 +2,7 @@
 (define-library (zilch lang ninja build)
  (import
   (scheme base) (scheme lazy) (scheme file)
+  (scheme case-lambda)
   (zilch file) (zilch magic) (scheme char)
   (zilch nix drv) (zilch nix path)
   (zilch nixpkgs) (zilch zexpr) (zilch vfs)
@@ -536,8 +537,10 @@
     (set-build-env-vfs! env (vfs-to-store (make-vfs filtered-vfs)))
 
     (define edge-ref
-     (lambda (path)
-       (define edge (mapping-ref edges path (lambda () (mapping-ref edges (normalize-path path) (lambda () (error "Target doesn't exist" path))))))
-       (cons (if (promise? (car edge)) (force (car edge)) (car edge)) (force (cdr edge)))))
+     (case-lambda
+      ((path) (edge-ref path #f))
+      ((path may-fail)
+       (define edge (mapping-ref edges path (lambda () (mapping-ref edges (normalize-path path) (lambda () (if may-fail #f (error "Target doesn't exist" path)))))))
+       (and edge (cons (if (promise? (car edge)) (force (car edge)) (car edge)) (force (cdr edge)))))))
     (define defaults (build-file-default-targets file))
     (values edge-ref defaults (lambda () (build-env-collected-deps env))))))