diff --git a/lang/ninja/src/build.sld b/lang/ninja/src/build.sld
index 1653b2f..29767f2 100644
--- a/lang/ninja/src/build.sld
+++ b/lang/ninja/src/build.sld
@@ -36,7 +36,9 @@
 
   ;; Helper to render nicer derivation names.
   (define (make-valid-store-path-string str)
-    (string-map (lambda (c) (if (is-valid-store-path-char c) c #\-)) (if (> (string-length str) 211) (string-copy str 0 211) str)))
+    (if (string=? "" str)
+      "zilch-ninja"
+      (string-map (lambda (c) (if (is-valid-store-path-char c) c #\-)) (if (> (string-length str) 211) (string-copy str 0 211) str))))
 
 
   (define (derivation-for-edge environment vfs relative-to-root edges current-edge)