diff --git a/piclib/prelude.scm b/piclib/prelude.scm
index 6245f678..d7a191f5 100644
--- a/piclib/prelude.scm
+++ b/piclib/prelude.scm
@@ -589,18 +589,6 @@
       s
       (fold f (f (car xs) s) (cdr xs))))
 
-;;; 6.2. Numbers
-
-; (import (only (scheme inexact) sqrt))
-(import (scheme inexact))
-
-(define (exact-integer-sqrt k)
-  (let ((n (exact (floor (sqrt k)))))
-    (values n (- k (square n)))))
-
-(export floor/ truncate/
-        exact-integer-sqrt)
-
 ;;; 6.3 Booleans
 
 (define (boolean=? . objs)
diff --git a/src/number.c b/src/number.c
index b7b32aea..8e15860a 100644
--- a/src/number.c
+++ b/src/number.c
@@ -661,6 +661,19 @@ pic_number_atan(pic_state *pic)
   }
 }
 
+static pic_value
+pic_number_exact_integer_sqrt(pic_state *pic)
+{
+  int k, n, m;
+
+  pic_get_args(pic, "i", &k);
+
+  n = sqrt(k);
+  m = k - n * n;
+
+  return pic_values2(pic, pic_int_value(n), pic_int_value(m));
+}
+
 static pic_value
 pic_number_square(pic_state *pic)
 {
@@ -840,6 +853,7 @@ pic_init_number(pic_state *pic)
   pic_defun(pic, "round", pic_number_round);
   pic_gc_arena_restore(pic, ai);
 
+  pic_defun(pic, "exact-integer-sqrt", pic_number_exact_integer_sqrt);
   pic_defun(pic, "square", pic_number_square);
   pic_defun(pic, "expt", pic_number_expt);
   pic_gc_arena_restore(pic, ai);