diff --git a/lib/scheme/extras.scm b/lib/scheme/extras.scm
index fbbf6cba..4ef1620a 100644
--- a/lib/scheme/extras.scm
+++ b/lib/scheme/extras.scm
@@ -35,9 +35,13 @@
 (define inexact exact->inexact)
 
 (define (boolean=? x y . o)
-  (and (eq? x y) (if (pair? o) (apply boolean=? y o) #t)))
+  (if (not (boolean? x))
+      (error "not a boolean" x)
+      (and (eq? x y) (if (pair? o) (apply boolean=? y o) #t))))
 (define (symbol=? x y . o)
-  (and (eq? x y) (if (pair? o) (apply symbol=? y o) #t)))
+  (if (not (symbol? x))
+      (error "not a symbol" x)
+      (and (eq? x y) (if (pair? o) (apply symbol=? y o) #t))))
 
 (define call/cc call-with-current-continuation)