diff --git a/Source/Data/CodeNote.cs b/Source/Data/CodeNote.cs
index 92b6d525..dd3f50fd 100644
--- a/Source/Data/CodeNote.cs
+++ b/Source/Data/CodeNote.cs
@@ -661,14 +661,14 @@ private static bool IsValue(Token token)
             if (token.StartsWith("0x"))
                 index += 2;
 
-            if (index == token.Length)
+            if (index == token.Length || !IsHexDigit(token[index]))
                 return false;
 
-            while (IsHexDigit(token[index]))
+            do
             {
                 if (++index == token.Length)
                     return true;
-            }
+            } while (IsHexDigit(token[index]));
 
             while (index < token.Length && Char.IsWhiteSpace(token[index]))
                 index++;
@@ -680,7 +680,7 @@ private static bool IsValue(Token token)
                 while (index < token.Length && Char.IsWhiteSpace(token[index]))
                     index++;
 
-                if (!IsHexDigit(token[index]))
+                if (index == token.Length || !IsHexDigit(token[index]))
                     return false;
 
                 do
diff --git a/Tests/Data/CodeNoteTests.cs b/Tests/Data/CodeNoteTests.cs
index 72a7a615..4d5a441f 100644
--- a/Tests/Data/CodeNoteTests.cs
+++ b/Tests/Data/CodeNoteTests.cs
@@ -371,5 +371,23 @@ public void TestPossibleButNotEnum()
             Assert.That(n.Size, Is.EqualTo(FieldSize.None));
             Assert.That(n.Values.Count(), Is.EqualTo(0));
         }
+
+        [Test]
+        public void TestUnboundedRangeEnums()
+        {
+            var n = new CodeNote(4, "[8-bit] Chars\n" +
+                "0-=!\n" + // 0 starts a range, but without an end, it's not valid
+                "-9=?\n" + // This dash is seen as an indent marker. the mapping "9=?" is processed.
+                "-=$\n" +  // These are all seen as prefix characters and are ignored.
+                "X=0-" +   // 0 starts a range, but without an end, it's not valid
+                "Y=-9" +   // 9 ends a range, but without a start, it's not valid
+                "Z=-");    // range has neither a start nor an end. it's not valid
+
+            Assert.That(n.Summary, Is.EqualTo("Chars"));
+            Assert.That(n.Size, Is.EqualTo(FieldSize.Byte));
+            Assert.That(n.Values.Count(), Is.EqualTo(1));
+            Assert.That(n.Values.First().Key, Is.EqualTo("9"));
+            Assert.That(n.Values.First().Value, Is.EqualTo("?"));
+        }
     }
 }