diff --git a/lang/rust/src/rust.sld b/lang/rust/src/rust.sld
index 60dc657..8708026 100644
--- a/lang/rust/src/rust.sld
+++ b/lang/rust/src/rust.sld
@@ -157,8 +157,11 @@
             (set! args (cons "-L" (cons #~,(string-append "all=" #$k) args)))
             (set! args (cons "-L" (cons #~,(string-append (car k) "=" #$(cdr k)) args)))))
         (rustc-params-search-path params)))
+    (unless (rustc-params-crate-type params) (error "crate-type unset"))
     (set! args (cons "--crate-type" (cons (symbol->string (rustc-params-crate-type params)) args)))
+    (unless (rustc-params-crate-name params) (error "crate-name unset"))
     (set! args (cons "--crate-name" (cons (rustc-params-crate-name params) args)))
+    (unless (rustc-params-edition params) (error "edition unset"))
     (set! args (cons "--edition" (cons (rustc-params-edition params) args)))
 
     (define-values (new-args outputs) (rustc-emits-as-list (rustc-params-emits params) args '()))