diff --git a/scheme/ikarus.numerics.ss b/scheme/ikarus.numerics.ss
index ca18674..f947186 100644
--- a/scheme/ikarus.numerics.ss
+++ b/scheme/ikarus.numerics.ss
@@ -1218,8 +1218,50 @@
         [(fixnum? n)
          (cond
            [(fixnum? m) ($fxmodulo n m)]
-           [else (error 'modulo "BUG: unsupported" m)])]
-        [else (error 'modulo "BUG: unsupported" n)])))
+           [(bignum? m) 
+            (if ($fx< n 0)
+                (if ($bignum-positive? m) 
+                    (foreign-call "ikrt_fxbnplus" n m)
+                    n)
+                (if ($bignum-positive? m) 
+                    n
+                    (foreign-call "ikrt_fxbnplus" n m)))]
+           [(flonum? m) 
+            (let ([v ($flonum->exact m)])
+              (cond
+                [(or (fixnum? v) (bignum? v)) 
+                 (inexact (modulo n v))]
+                [else
+                 (error 'modulo "not an integer" m)]))]
+           [(ratnum? m) (error 'modulo "not an integer" m)]
+           [else (error 'modulo "not a number" m)])]
+        [(bignum? n)
+         (cond
+           [(fixnum? m) 
+            (foreign-call "ikrt_bnfx_modulo" n m)]
+           [(bignum? m) 
+            (error 'modulo
+              "BUG: two bignum arguments are not yet implemented"
+              n m)
+            (foreign-call "ikrt_bnbn_modulo" n m)]
+           [(flonum? m) 
+            (let ([v ($flonum->exact m)])
+              (cond
+                [(or (fixnum? v) (bignum? v)) 
+                 (inexact (modulo n v))]
+                [else
+                 (error 'modulo "not an integer" m)]))] 
+           [(ratnum? m) (error 'modulo "not an integer" m)]
+           [else (error 'modulo "not a number" m)])]
+        [(flonum? n) 
+         (let ([v ($flonum->exact n)])
+           (cond
+             [(or (fixnum? v) (bignum? v)) 
+              (inexact (modulo v m))]
+             [else
+              (error 'modulo "not an integer" n)]))]
+        [(ratnum? n) (error 'modulo "not an integer" n)]
+        [else (error 'modulo "not a number" n)])))
 
   (define-syntax mk<
     (syntax-rules ()
diff --git a/scheme/run-tests.ss b/scheme/run-tests.ss
index 30f9797..d1f4a08 100755
--- a/scheme/run-tests.ss
+++ b/scheme/run-tests.ss
@@ -1,4 +1,4 @@
-#!/usr/bin/env ikarus --r6rs-script
+#!../src/ikarus -b ikarus.boot --r6rs-script
 
 ;;; Ikarus Scheme -- A compiler for R6RS Scheme.
 ;;; Copyright (C) 2006,2007  Abdulaziz Ghuloum
@@ -23,7 +23,7 @@
         (tests strings)
         (tests hashtables)
         ;(tests numbers)
-        ;(tests bignums)
+        (tests bignums)
         (tests fxcarry)
         (tests bignum-to-flonum)
         (tests string-to-number))
@@ -48,7 +48,7 @@
 (test-bignum-to-flonum)
 (test-string-to-number)
 ;(test-div-and-mod)
-;(test-bignums)
+(test-bignums)
 (test-fxcarry)
 (test-lists)
 (test-hashtables)
diff --git a/scheme/tests/bignums.ss b/scheme/tests/bignums.ss
new file mode 100644
index 0000000..3475281
--- /dev/null
+++ b/scheme/tests/bignums.ss
@@ -0,0 +1,95 @@
+(library (tests bignums)
+  (export test-bignums)
+  (import (ikarus) (tests framework))
+
+  (define-tests test-bignums
+    ; first, some simple quotients
+    [(lambda (x) (= x 101))  (quotient 348972 3434)]
+    [(lambda (x) (= x -101)) (quotient -348972 3434)]
+    [(lambda (x) (= x -101)) (quotient 348972 -3434)]
+    [(lambda (x) (= x 101))  (quotient -348972 -3434)]
+    ; then bump first argument to a small bignum:
+    [(lambda (x) (= x 2255760))  (quotient 536870912 238)]
+    [(lambda (x) (= x -2255760)) (quotient -536870912 238)]
+    [(lambda (x) (= x -2255760)) (quotient 536870912 -238)]
+    [(lambda (x) (= x 2255760))  (quotient -536870912 -238)]
+    ; then bump first argument to a big bignum:
+    [(lambda (x) (= x 1652556267336712615))
+     (quotient 536870912238479837489374 324873)]
+    [(lambda (x) (= x -1652556267336712615))
+     (quotient -536870912238479837489374 324873)]
+    [(lambda (x) (= x -1652556267336712615))
+     (quotient 536870912238479837489374 -324873)]
+    [(lambda (x) (= x 1652556267336712615))
+     (quotient -536870912238479837489374 -324873)]
+    ; then make both arguments bignums, but result fixnum:
+    [(lambda (x) (= x 165)) 
+     (quotient 536870912238479837489374 3248732398479823749283)]
+    [(lambda (x) (= x -165)) 
+     (quotient -536870912238479837489374 3248732398479823749283)]
+    [(lambda (x) (= x -165)) 
+     (quotient 536870912238479837489374 -3248732398479823749283)]
+    [(lambda (x) (= x 165)) 
+     (quotient -536870912238479837489374 -3248732398479823749283)]
+    ; then both arguments and result are all bignums:
+    [(lambda (x) (= x 1652555047284588078))
+     (quotient 5368709122384798374893743894798327498234 3248732398479823749283)]
+    [(lambda (x) (= x -1652555047284588078))
+     (quotient -5368709122384798374893743894798327498234 3248732398479823749283)]
+    [(lambda (x) (= x -1652555047284588078))
+     (quotient 5368709122384798374893743894798327498234 -3248732398479823749283)]
+    [(lambda (x) (= x 1652555047284588078))
+     (quotient -5368709122384798374893743894798327498234 -3248732398479823749283)]
+
+
+
+
+    [(lambda (x) (= x 23))            (remainder 23 349839489348)]
+    [(lambda (x) (= x -23))           (remainder -23 349839489348)]
+    [(lambda (x) (= x 23))            (remainder 23 -349839489348)]
+    [(lambda (x) (= x -23))           (remainder -23 -349839489348)]
+    
+
+    ;;; Next, modulo
+    ; first, some simple arguments
+    [(lambda (x) (= x 2138))  (modulo 348972 3434)]
+    [(lambda (x) (= x 1296))  (modulo -348972 3434)]
+    [(lambda (x) (= x -1296)) (modulo 348972 -3434)]
+    [(lambda (x) (= x -2138)) (modulo -348972 -3434)]
+    ; then bignum second argument: can be done with +/-
+    [(lambda (x) (= x 349839489325))  (modulo -23 349839489348)]
+    [(lambda (x) (= x -23))           (modulo -23 -349839489348)]
+    [(lambda (x) (= x 23))            (modulo 23 349839489348)]
+    [(lambda (x) (= x -349839489325)) (modulo 23 -349839489348)]
+
+    ; then bump first argument to a small bignum:
+    [(lambda (x) (= x 32))  (remainder 536870912 238)]
+    [(lambda (x) (= x -32)) (remainder -536870912 238)]
+    [(lambda (x) (= x 32))  (remainder 536870912 -238)]
+    [(lambda (x) (= x -32)) (remainder -536870912 -238)]
+
+    [(lambda (x) (= x 32))   (modulo 536870912 238)]
+    [(lambda (x) (= x 206))  (modulo -536870912 238)]
+    [(lambda (x) (= x -206)) (modulo 536870912 -238)]
+    [(lambda (x) (= x -32))  (modulo -536870912 -238)]
+    ; then bump first argument to a big bignum:
+    [(lambda (x) (= x 116479))
+     (modulo 536870912238479837489374 324873)]
+    [(lambda (x) (= x 208394))
+     (modulo -536870912238479837489374 324873)]
+    [(lambda (x) (= x -208394))
+     (modulo 536870912238479837489374 -324873)]
+    [(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)]
+    ))
+
+
diff --git a/src/ikarus-numerics.c b/src/ikarus-numerics.c
index ddd74f3..fb98973 100644
--- a/src/ikarus-numerics.c
+++ b/src/ikarus-numerics.c
@@ -1435,6 +1435,43 @@ ikrt_bnfxdivrem(ikp x, ikp y, ikpcb* pcb){
   return p+pair_tag;
 }
 
+ikp
+ikrt_bnfx_modulo(ikp x, ikp y, ikpcb* pcb){
+  int yint = unfix(y);
+  mp_limb_t* s2p = (mp_limb_t*)(x+off_bignum_data);
+  ikp fst = ref(x, -vector_tag);
+  mp_size_t s2n = ((unsigned int) fst) >> bignum_length_shift;
+  if(yint < 0){
+    if(((unsigned int) fst) & bignum_sign_mask){
+      /* x negative, y negative */
+      mp_limb_t m = mpn_mod_1(s2p, s2n, -yint);
+      return fix(-m);
+    } else {
+      /* x positive, y negative */
+      mp_limb_t m = mpn_mod_1(s2p, s2n, -yint);
+      return fix(yint+m);
+    }
+  } else {
+    if(((unsigned int) fst) & bignum_sign_mask){
+      /* x negative, y positive */
+      mp_limb_t m = mpn_mod_1(s2p, s2n, yint);
+      return fix(yint-m);
+    } else {
+      /* x positive, y positive */
+      mp_limb_t m = mpn_mod_1(s2p, s2n, yint);
+      return fix(m);
+    }
+  }
+}
+
+ikp
+ikrt_bnbn_modulo(ikp x, ikp y, ikpcb* pcb){
+  fprintf(stderr, "error in bnbnmodulo\n");
+  exit(-1);
+}
+
+
+
 
 ikp
 ikrt_bignum_to_bytevector(ikp x, ikpcb* pcb){