Index: numbers-c.c
===================================================================
--- numbers-c.c	(revision 9881)
+++ numbers-c.c	(working copy)
@@ -55,10 +55,23 @@
 }
 
 
+static double
+mpq_get_d_accurately(mpq_t rat)
+{
+  mpz_t *num, *den;
+  num = mpq_numref(rat);
+  den = mpq_denref(rat);
+  if (mpz_fits_slong_p(*num) && mpz_fits_slong_p(*den)) {
+    return (double) (mpz_get_d(*num) / mpz_get_d(*den));
+  } else {
+    return mpq_get_d(rat);
+  }
+}
+
 static C_word
 rat_to_flo(C_word **p, C_word n, C_word rat)
 {
-  return C_flonum(p, mpq_get_d(rat_of(rat)));
+  return C_flonum(p, mpq_get_d_accurately(rat_of(rat)));
 }
 
 
@@ -1189,7 +1202,7 @@
       return C_mk_bool(C_flonum_magnitude(x) == C_flonum_magnitude(y));
 
     case C_fix(RAT):
-      return C_mk_bool(C_flonum_magnitude(x) == mpq_get_d(rat_of(y)));
+      return C_mk_bool(C_flonum_magnitude(x) == mpq_get_d_accurately(rat_of(y)));
 
     default: return C_SCHEME_FALSE;
     }
@@ -1210,7 +1223,7 @@
   case C_fix(RAT):
     switch(ty) {
     case C_fix(FLO):
-      return C_mk_bool(mpq_get_d(rx) == C_flonum_magnitude(y));
+      return C_mk_bool(mpq_get_d_accurately(rx) == C_flonum_magnitude(y));
 
     case C_fix(RAT):
       { defrat(ry, y);