diff --git a/src/portableML/mosml/Arbintcore.sig b/src/portableML/mosml/Arbintcore.sig
index c0e4902fe3..bb8a2b021c 100644
--- a/src/portableML/mosml/Arbintcore.sig
+++ b/src/portableML/mosml/Arbintcore.sig
@@ -16,6 +16,7 @@ sig
   val fromNat    : num -> int
   val toInt      : int -> Int.int
   val toNat      : int -> num
+  val toReal     : int -> real
 
   val +          : (int * int) -> int
   val -          : (int * int) -> int
diff --git a/src/portableML/mosml/Arbintcore.sml b/src/portableML/mosml/Arbintcore.sml
index 7c44f9877e..03e200156e 100644
--- a/src/portableML/mosml/Arbintcore.sml
+++ b/src/portableML/mosml/Arbintcore.sml
@@ -112,6 +112,9 @@ fun fromInt n =
   if (Int.<(n,0)) then (false, Arbnumcore.fromInt(Int.-(0, n)))
   else (true, Arbnumcore.fromInt n)
 
+fun toReal (true,n) = Arbnumcore.toReal n
+  | toReal (false,n) = Real.~(Arbnumcore.toReal n)
+
 
 fun min (i,j) = if i < j then i else j
 fun max (i,j) = if i < j then j else i
diff --git a/src/portableML/mosml/Arbnumcore.sig b/src/portableML/mosml/Arbnumcore.sig
index 1989a6e847..9db797d4e8 100644
--- a/src/portableML/mosml/Arbnumcore.sig
+++ b/src/portableML/mosml/Arbnumcore.sig
@@ -30,9 +30,9 @@ sig
 
   val fromInt     : int -> num    (* raises Overflow if i < 0 *)
   val toInt       : num -> int    (* raises Overflow if n > maxInt *)
+  val toReal      : num -> real   (* raises Overflow if real calcs do so; no posinf for you! *)
 
   val floor       : real -> num   (* raises Overflow if r < 0 *)
-  val toReal      : num -> real
 
   val asList      : num -> int list
 
diff --git a/src/portableML/mosml/Arbnumcore.sml b/src/portableML/mosml/Arbnumcore.sml
index b0526768c1..1ca679e618 100644
--- a/src/portableML/mosml/Arbnumcore.sml
+++ b/src/portableML/mosml/Arbnumcore.sml
@@ -475,6 +475,14 @@ in
   val toHexString = toBaseString (fromInt 16)
 end
 
+fun toReal0 f A is =
+    case is of
+        [] => A
+      | i :: rest => toReal0 (Real.*(f,Real.fromInt BASE))
+                             (Real.+(A,Real.*(f,Real.fromInt i)))
+                             rest
+fun toReal an = toReal0 1.0 0.0 an
+
 fun isqrt n =
    if n < two
       then n