diff --git a/scheme/ikarus.numerics.ss b/scheme/ikarus.numerics.ss
index f947186..6bd04ee 100644
--- a/scheme/ikarus.numerics.ss
+++ b/scheme/ikarus.numerics.ss
@@ -1240,10 +1240,17 @@
            [(fixnum? m) 
             (foreign-call "ikrt_bnfx_modulo" n m)]
            [(bignum? m) 
-            (error 'modulo
-              "BUG: two bignum arguments are not yet implemented"
-              n m)
-            (foreign-call "ikrt_bnbn_modulo" n m)]
+            (if ($bignum-positive? n) 
+                (if ($bignum-positive? m) 
+                    (remainder n m)
+                    (+ m (remainder n m)))
+                (if ($bignum-positive? m)
+                    (+ m (remainder n m))
+                    (remainder n m)))]
+            ;(error 'modulo
+            ;  "BUG: two bignum arguments are not yet implemented"
+            ;  n m)
+            ;(foreign-call "ikrt_bnbn_modulo" n m)]
            [(flonum? m) 
             (let ([v ($flonum->exact m)])
               (cond
diff --git a/scheme/tests/bignums.ss b/scheme/tests/bignums.ss
index 3475281..5bb2ec2 100644
--- a/scheme/tests/bignums.ss
+++ b/scheme/tests/bignums.ss
@@ -82,14 +82,14 @@
     [(lambda (x) (= x -116479))
      (modulo -536870912238479837489374 -324873)]
     ; then make both arguments bignums
-    ;[(lambda (x) (= x 830066489308918857679)) 
-    ; (modulo 536870912238479837489374 3248732398479823749283)]
-    ;[(lambda (x) (= x 2418665909170904891604)) 
-    ; (modulo -536870912238479837489374 3248732398479823749283)]
-    ;[(lambda (x) (= x -2418665909170904891604)) 
-    ; (modulo 536870912238479837489374 -3248732398479823749283)]
-    ;[(lambda (x) (= x -830066489308918857679))
-    ; (modulo -536870912238479837489374 -3248732398479823749283)]
+    [(lambda (x) (= x 830066489308918857679)) 
+     (modulo 536870912238479837489374 3248732398479823749283)]
+    [(lambda (x) (= x -2418665909170904891604)) 
+     (modulo 536870912238479837489374 -3248732398479823749283)]
+    [(lambda (x) (= x 2418665909170904891604)) 
+     (modulo -536870912238479837489374 3248732398479823749283)]
+    [(lambda (x) (= x -830066489308918857679))
+     (modulo -536870912238479837489374 -3248732398479823749283)]
     ))
 
 
diff --git a/src/ikarus-numerics.c b/src/ikarus-numerics.c
index fb98973..12ff1fd 100644
--- a/src/ikarus-numerics.c
+++ b/src/ikarus-numerics.c
@@ -1464,11 +1464,6 @@ ikrt_bnfx_modulo(ikp x, ikp y, ikpcb* pcb){
   }
 }
 
-ikp
-ikrt_bnbn_modulo(ikp x, ikp y, ikpcb* pcb){
-  fprintf(stderr, "error in bnbnmodulo\n");
-  exit(-1);
-}