diff --git a/src/bigints.nim b/src/bigints.nim
index 9ef5abb..21e0226 100644
--- a/src/bigints.nim
+++ b/src/bigints.nim
@@ -1,6 +1,6 @@
 ## Arbitrary precision integers.
 
-import std/[algorithm, bitops, math, options]
+import std/[algorithm, bitops, fenv, math, options]
 
 type
   BigInt* = object
@@ -1140,6 +1140,11 @@ func fastLog2*(a: BigInt): int =
     return -1
   bitops.fastLog2(a.limbs[^1]) + 32*(a.limbs.high)
 
+func toBiggestFloat*(x: BigInt): BiggestFloat =
+  let l = mantissaDigits(BiggestFloat)+1
+  let shift = max(fastLog2(x) - l, 0)
+  let mantissa = BiggestFloat(toInt[BiggestInt](x shr shift).get())
+  result = mantissa * pow(2.0, BiggestFloat(shift))
 
 func invmod*(a, modulus: BigInt): BigInt =
   ## Compute the modular inverse of `a` modulo `modulus`.
diff --git a/tests/tbigints.nim b/tests/tbigints.nim
index 3b3a59d..d3f8be9 100644
--- a/tests/tbigints.nim
+++ b/tests/tbigints.nim
@@ -786,6 +786,16 @@ proc main() =
     doAssert pred(a, 3) == initBigInt(4)
     doAssert succ(a, 3) == initBigInt(10)
 
+  block: # to float
+    doAssert toBiggestFloat(initBigInt("0")) == 0.0
+    doAssert toBiggestFloat(initBigInt("1")) == 1.0
+    doAssert toBiggestFloat(initBigInt("-1")) == -1.0
+    doAssert toBiggestFloat(initBigInt(BiggestInt.high)) == BiggestInt.high.toBiggestFloat
+    doAssert toBiggestFloat(initBigInt(BiggestInt.low)) == BiggestInt.low.toBiggestFloat
+    doAssert toBiggestFloat(initBigInt(BiggestInt.high) * initBigInt(4)) == BiggestInt.high.toBiggestFloat * 4.0
+    doAssert toBiggestFloat(initBigInt(BiggestInt.low) * initBigInt(4)) == BiggestInt.low.toBiggestFloat * 4.0
+    doAssert toBiggestFloat(initBigInt("17976931348623157") * initBigInt(10).pow(292)) == 17976931348623157e292
+
 
 static: main()
 main()