diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index d105d1a..919c77c 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -29,10 +29,11 @@ jobs:
 
       # ----- Install WiX v4 -----------------------------------------------
       - name: Install WiX Toolset v4
-        run: dotnet tool install --global wix
+        run: dotnet tool install --global wix --version 4.0.5
 
       - name: Add WiX UI extension
-        run: wix extension add WixToolset.UI.wixext
+        working-directory: installer
+        run: wix extension add WixToolset.UI.wixext/4.0.5
 
       # ----- Determine version from git tag --------------------------------
       # Tag v0.75 becomes MSI version 0.75.0.0 (4-part dotted form required)
diff --git a/app.h b/include/app.h
similarity index 100%
rename from app.h
rename to include/app.h
diff --git a/config.h b/include/config.h
similarity index 100%
rename from config.h
rename to include/config.h
diff --git a/fileops.h b/include/fileops.h
similarity index 100%
rename from fileops.h
rename to include/fileops.h
diff --git a/input.h b/include/input.h
similarity index 100%
rename from input.h
rename to include/input.h
diff --git a/keys.h b/include/keys.h
similarity index 100%
rename from keys.h
rename to include/keys.h
diff --git a/packcom.h b/include/packcom.h
similarity index 100%
rename from packcom.h
rename to include/packcom.h
diff --git a/platform.h b/include/platform.h
similarity index 96%
rename from platform.h
rename to include/platform.h
index 634af04..946910a 100644
--- a/platform.h
+++ b/include/platform.h
@@ -11,7 +11,10 @@
 #include <cstdint>
 
 #ifdef _WIN32
-#  define PACKCOM_WINDOWS
+#  ifndef PACKCOM_WINDOWS
+#    define PACKCOM_WINDOWS
+#  endif
+#  define NOMINMAX
 #  include <windows.h>
 #  include <conio.h>
 #else
@@ -75,7 +78,7 @@ void beep();
 
 #ifdef PACKCOM_WINDOWS
 using SerialHandle = HANDLE;
-constexpr SerialHandle INVALID_SERIAL = INVALID_HANDLE_VALUE;
+static const SerialHandle INVALID_SERIAL = INVALID_HANDLE_VALUE;
 #else
 using SerialHandle = int;
 constexpr SerialHandle INVALID_SERIAL = -1;
diff --git a/serial.h b/include/serial.h
similarity index 100%
rename from serial.h
rename to include/serial.h
diff --git a/terminal.h b/include/terminal.h
similarity index 100%
rename from terminal.h
rename to include/terminal.h
diff --git a/yapp.h b/include/yapp.h
similarity index 100%
rename from yapp.h
rename to include/yapp.h
diff --git a/installer/PackCom.wxs b/installer/PackCom.wxs
index 44fb2b9..ac03c78 100644
--- a/installer/PackCom.wxs
+++ b/installer/PackCom.wxs
@@ -26,18 +26,18 @@
     <!-- Embed all files inside the MSI -->
     <MediaTemplate EmbedCab="yes" />
 
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <!--  UI  –  WiX built-in WixUI_Minimal dialog set                       -->
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <ui:WixUI Id="WixUI_InstallDir" />
     <Property Id="WIXUI_INSTALLDIR" Value="INSTALLFOLDER" />
 
     <!-- Licence text shown in the UI -->
     <WixVariable Id="WixUILicenseRtf" Value="..\LICENSE.rtf" />
 
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <!--  Directory structure                                                 -->
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <StandardDirectory Id="ProgramFiles64Folder">
       <Directory Id="INSTALLFOLDER" Name="PackCom" />
     </StandardDirectory>
@@ -48,9 +48,9 @@
 
     <StandardDirectory Id="DesktopFolder" />
 
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <!--  Components                                                          -->
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <ComponentGroup Id="ProductComponents" Directory="INSTALLFOLDER">
 
       <!-- Main executable -->
@@ -108,9 +108,9 @@
 
     </ComponentGroup>
 
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <!--  Feature tree                                                        -->
-    <!-- ------------------------------------------------------------------ -->
+    <!-- ============================================================ -->
     <Feature Id="ProductFeature"
              Title="PackCom"
              Level="1"
diff --git a/app.cpp b/src/app.cpp
similarity index 100%
rename from app.cpp
rename to src/app.cpp
diff --git a/config.cpp b/src/config.cpp
similarity index 100%
rename from config.cpp
rename to src/config.cpp
diff --git a/fileops.cpp b/src/fileops.cpp
similarity index 100%
rename from fileops.cpp
rename to src/fileops.cpp
diff --git a/input.cpp b/src/input.cpp
similarity index 100%
rename from input.cpp
rename to src/input.cpp
diff --git a/main.cpp b/src/main.cpp
similarity index 100%
rename from main.cpp
rename to src/main.cpp
diff --git a/platform.cpp b/src/platform.cpp
similarity index 100%
rename from platform.cpp
rename to src/platform.cpp
diff --git a/serial.cpp b/src/serial.cpp
similarity index 100%
rename from serial.cpp
rename to src/serial.cpp
diff --git a/terminal.cpp b/src/terminal.cpp
similarity index 100%
rename from terminal.cpp
rename to src/terminal.cpp
diff --git a/yapp.cpp b/src/yapp.cpp
similarity index 100%
rename from yapp.cpp
rename to src/yapp.cpp