2 files changed, 35 insertions, 9 deletions

diff --git a/src/WixToolset.Converters/WixConverter.cs b/src/WixToolset.Converters/WixConverter.cs
index 18cd7115..4d5564b4 100644
--- a/src/WixToolset.Converters/WixConverter.cs
+++ b/src/WixToolset.Converters/WixConverter.cs
@@ -636,8 +636,8 @@ namespace WixToolset.Converters
                 var win64 = element.Attribute("Win64");
                 if (win64 != null && this.OnError(ConverterTestType.Win64AttributeRenamed, element, "The Win64 attribute has been renamed. Use the Bitness attribute instead."))
                 {
-                    var value = win64.Value;
-                    element.Add(new XAttribute("Bitness", value == "yes" ? "always64" : "always32"));
+                    var value = this.UpdateWin64ValueToBitnessValue(win64);
+                    element.Add(new XAttribute("Bitness", value));
                     win64.Remove();
                 }
             }
@@ -755,8 +755,8 @@ namespace WixToolset.Converters
             var win64 = element.Attribute("Win64");
             if (win64 != null && this.OnError(ConverterTestType.Win64AttributeRenamed, element, "The Win64 attribute has been renamed. Use the Bitness attribute instead."))
             {
-                var value = win64.Value;
-                element.Add(new XAttribute("Bitness", value == "yes" ? "always64" : "always32"));
+                var value = this.UpdateWin64ValueToBitnessValue(win64);
+                element.Add(new XAttribute("Bitness", value));
                 win64.Remove();
             }
         }
@@ -1104,8 +1104,8 @@ namespace WixToolset.Converters
                 var win64 = element.Attribute("Win64");
                 if (win64 != null && this.OnError(ConverterTestType.Win64AttributeRenamed, element, "The Win64 attribute has been renamed. Use the Bitness attribute instead."))
                 {
-                    var value = win64.Value;
-                    element.Add(new XAttribute("Bitness", value == "yes" ? "always64" : "always32"));
+                    var value = this.UpdateWin64ValueToBitnessValue(win64);
+                    element.Add(new XAttribute("Bitness", value));
                     win64.Remove();
                 }
             }
@@ -1296,8 +1296,8 @@ namespace WixToolset.Converters
                 var win64 = element.Attribute("Win64");
                 if (win64 != null && this.OnError(ConverterTestType.Win64AttributeRenamed, element, "The Win64 attribute has been renamed. Use the Bitness attribute instead."))
                 {
-                    var value = win64.Value;
-                    element.Add(new XAttribute("Bitness", value == "yes" ? "always64" : "always32"));
+                    var value = this.UpdateWin64ValueToBitnessValue(win64);
+                    element.Add(new XAttribute("Bitness", value));
                     win64.Remove();
                 }
 
@@ -1341,6 +1341,21 @@ namespace WixToolset.Converters
             }
         }
 
+        private string UpdateWin64ValueToBitnessValue(XAttribute xWin64Attribute)
+        {
+            var value = xWin64Attribute.Value ?? String.Empty;
+            switch (value)
+            {
+                case "yes":
+                    return "always64";
+                case "no":
+                    return "always32";
+                default:
+                    this.OnError(ConverterTestType.Win64AttributeRenameCannotBeAutomatic, xWin64Attribute, "Breaking change: The Win64 attribute's value '{0}' cannot be converted automatically to the new Bitness attribute.", value);
+                    return value;
+            }
+        }
+
         private IEnumerable<ConverterTestType> YieldConverterTypes(IEnumerable<string> types)
         {
             if (null != types)
@@ -1795,6 +1810,11 @@ namespace WixToolset.Converters
             /// The Win64 attribute has been renamed. Use the Bitness attribute instead.
             /// </summary>
             Win64AttributeRenamed,
+
+            /// <summary>
+            /// Breaking change: The Win64 attribute's value '{0}' cannot be converted automatically to the new Bitness attribute.
+            /// </summary>
+            Win64AttributeRenameCannotBeAutomatic,
         }
     }
 }
diff --git a/src/test/WixToolsetTest.Converters/BitnessFixture.cs b/src/test/WixToolsetTest.Converters/BitnessFixture.cs
index 9996806d..e45a9388 100644
--- a/src/test/WixToolsetTest.Converters/BitnessFixture.cs
+++ b/src/test/WixToolsetTest.Converters/BitnessFixture.cs
@@ -27,6 +27,9 @@ namespace WixToolsetTest.Converters
                 "    <Component Win64='yes'>",
                 "        <File Source='64bit.exe' />",
                 "    </Component>",
+                "    <Component Win64='$(var.Win64)'>",
+                "        <File Source='unconvert.exe' />",
+                "    </Component>",
                 "  </Fragment>",
                 "</Wix>");
 
@@ -43,6 +46,9 @@ namespace WixToolsetTest.Converters
                 "    <Component Bitness=\"always64\">",
                 "        <File Id=\"_64bit.exe\" Source=\"64bit.exe\" />",
                 "    </Component>",
+                "    <Component Bitness=\"$(var.Win64)\">",
+                "        <File Id=\"unconvert.exe\" Source=\"unconvert.exe\" />",
+                "    </Component>",
                 "  </Fragment>",
                 "</Wix>"
             };
@@ -53,7 +59,7 @@ namespace WixToolsetTest.Converters
             var converter = new WixConverter(messaging, 2, null, null);
 
             var errors = converter.ConvertDocument(document);
-            Assert.Equal(7, errors);
+            Assert.Equal(10, errors);
 
             var actualLines = UnformattedDocumentLines(document);
             WixAssert.CompareLineByLine(expected, actualLines);