diff --git a/lib/srfi/229.sld b/lib/srfi/229.sld
index 3018da15..b19589c2 100644
--- a/lib/srfi/229.sld
+++ b/lib/srfi/229.sld
@@ -22,6 +22,7 @@
       (and (procedure? f)
            (let ((vars (procedure-vars f)))
              (and (vector? vars)
+                  (> (vector-length vars) 1)
                   (eq? procedure-tag-object
                        (vector-ref vars (- (vector-length vars) 1)))))))
     (define (procedure-tag f)
diff --git a/lib/srfi/229/test.sld b/lib/srfi/229/test.sld
index 754f3f9b..be3408c2 100644
--- a/lib/srfi/229/test.sld
+++ b/lib/srfi/229/test.sld
@@ -15,6 +15,7 @@
                       (x)
                       (* x x)))
         (test-assert (procedure/tag? f))
+        (test-not (procedure/tag? (lambda (x) (* x x))))
         (test 9 (f 3))
         (test 42 (procedure-tag f))
         (test-not (eqv? f f*))