diff --git a/core/src/main/scala/simpleivr/Ivr.scala b/core/src/main/scala/simpleivr/Ivr.scala
index 34c0fe6..b8982c2 100644
--- a/core/src/main/scala/simpleivr/Ivr.scala
+++ b/core/src/main/scala/simpleivr/Ivr.scala
@@ -62,7 +62,7 @@ class Ivr(sayables: Sayables) {
       case (acc, x)                                            =>
         def sayDigitOrDigits(n: Int) = numberWords(n) & (if (n == 1) `digit` else `digits`)
 
-        val str = acc + x.filter(_ != '#').mkString
+        val str = acc + x.filter(_ != DTMF.`#`).mkString
         val validated =
           if ((min == max) && (str.length != min)) Left(`You must enter ` & sayDigitOrDigits(min))
           else if (str.length < min) Left(`You must enter at least` & sayDigitOrDigits(min))
diff --git a/core/src/main/scala/simpleivr/Sayables.scala b/core/src/main/scala/simpleivr/Sayables.scala
index 3c0017c..19eb71e 100644
--- a/core/src/main/scala/simpleivr/Sayables.scala
+++ b/core/src/main/scala/simpleivr/Sayables.scala
@@ -101,7 +101,13 @@ abstract class Sayables(val audioFileBackend: AudioFileBackend) extends Speaks {
     }
   }
 
-  def digitWords(s: String): Sayable = Sayable.Many(s.toSeq.map(c => numberWords(c - '0')))
+  def digitWords(digitString: String): Sayable =
+    Sayable.Many(
+      digitString
+        .map(_ - '0')
+        .filter(d => d >= 0 && d <= 9)
+        .map(numberWords)
+    )
 
   def dtmfWord(c: DTMF): Sayable = c match {
     case DTMF.`#` => `pound`
diff --git a/version.sbt b/version.sbt
index 01120e3..b6bfa82 100644
--- a/version.sbt
+++ b/version.sbt
@@ -1 +1 @@
-ThisBuild / version := "0.5.2"
+ThisBuild / version := "0.5.2.1"