diff --git a/src/main/scala/dsptools/tester/DspTesterUtilities.scala b/src/main/scala/dsptools/tester/DspTesterUtilities.scala
index 4b349363..a4d34776 100644
--- a/src/main/scala/dsptools/tester/DspTesterUtilities.scala
+++ b/src/main/scala/dsptools/tester/DspTesterUtilities.scala
@@ -13,14 +13,14 @@ import chisel3.iotesters.TestersCompatibility
 
 object DspTesterUtilities {
  
-  // Converts negative Double's to their 2's complement BigInt equivalents 
+  // Converts signed Double's to their 2's complement BigInt equivalents (unsigned)
   // (totalWidth, fractionalWidth of some FixedPoint)
-  def toBigIntUnsigned(x: Double, totalWidth: Int, fractionalWidth: Int): BigInt = {
+  def signedToBigIntUnsigned(x: Double, totalWidth: Int, fractionalWidth: Int): BigInt = {
     val bi = FixedPoint.toBigInt(x, fractionalWidth)
     val neg = bi < 0
-    val neededWidth = if (neg) bi.bitLength + 1 else bi.bitLength
+    val neededWidth = bi.bitLength + 1
     require(neededWidth <= totalWidth, "Double -> BigInt width larger than total width allocated!")
-    if (neg) (BigInt(1) << neededWidth) + bi 
+    if (neg) (BigInt(1) << totalWidth) + bi
     else bi
   }
 
@@ -119,4 +119,4 @@ object DspTesterUtilities {
     }
   }
 
-}
\ No newline at end of file
+}
diff --git a/src/test/scala/dsptools/DspTesterSpec.scala b/src/test/scala/dsptools/DspTesterSpec.scala
index 12ede60d..f54f4631 100644
--- a/src/test/scala/dsptools/DspTesterSpec.scala
+++ b/src/test/scala/dsptools/DspTesterSpec.scala
@@ -2,6 +2,68 @@
 
 package dsptools
 
+import DspTesterUtilities._
+import org.scalatest.{FlatSpec, Matchers}
+import scala.math.{pow, abs}
+
 class DspTesterSpec {
 
 }
+
+class DspTesterUtilitiesSpec extends FlatSpec with Matchers {
+
+  behavior of "Tester Converters"
+
+  it should "convert positive and negative doubles to their BigInt, fixed point equivalents" in {
+
+    def check_conversion(value: Double, totalWidth: Int, fractionalWidth: Int, verbose: Boolean = false): Unit = {
+      if (verbose) { println(s"value = $value\ntotal width = $totalWidth\nfractional width = $fractionalWidth") }
+      var bi = signedToBigIntUnsigned(value, totalWidth, fractionalWidth)
+      if (verbose) { println(s"result = $bi") }
+      // check sign, flip if necessary
+      if (totalWidth > 0 && bi.testBit(totalWidth-1)) {
+        bi = -1 * ((bi ^ ((BigInt(1) << totalWidth) - 1)) + 1)
+      }
+      val bid = bi.toDouble / (BigInt(1) << fractionalWidth).toDouble
+      if (verbose) { println(s"back to double = $bid") }
+      val comp = scala.math.abs(bid-value)
+      if (verbose) { println(s"comp = $comp") }
+      val ref = scala.math.pow(2, -fractionalWidth)
+      if (verbose) { println(s"ref = $ref") }
+      require(abs(bid-value) < pow(2, -fractionalWidth))
+    }
+
+    // integers
+    var width = 14
+    for (i <- -pow(2,width-1).toInt until pow(2,width-1).toInt) {
+      check_conversion(i, width, 0)
+    }
+
+    // big integers
+    width = 40
+    for (i <- -pow(2,width-1).toInt to pow(2,width-1).toInt by pow(2, 20).toInt) {
+      check_conversion(i, width, 0)
+    }
+
+    // total > fractional
+    width = 19
+    var fract = 8
+    for (i <- -pow(2,width-fract-1) to pow(2,width-fract-1)-1 by 1.0/fract*0.9) {
+      check_conversion(i, width, fract)
+    }
+
+    // total < fractional
+    width = 11
+    fract = 17
+    for (i <- -pow(2,width-fract-1) to pow(2,width-fract-1)-1 by 1.0/fract*0.9) {
+      check_conversion(i, width, fract)
+    }
+
+  }
+
+  it should "fail to convert doubles to BigInts when not enough space is supplied" in {
+    intercept[IllegalArgumentException] { signedToBigIntUnsigned(2.0, 4, 2) }
+    intercept[IllegalArgumentException] { signedToBigIntUnsigned(-2.25, 4, 2) }
+  }
+
+}