diff --git a/data/misc/meson.build b/data/misc/meson.build
index fa337a8f..a4d4ac70 100644
--- a/data/misc/meson.build
+++ b/data/misc/meson.build
@@ -1,5 +1,6 @@
 appdir = join_paths(get_option('datadir'), 'applications')
 metainfodir = join_paths(get_option('datadir'), 'metainfo')
+mimedir = join_paths(get_option('datadir'), 'mime', 'packages')
 desktop_utils = find_program('desktop-file-validate', required: false)
 
 if get_option('gtk-frontend')
@@ -42,6 +43,10 @@ if get_option('gtk-frontend')
     install_dir: appdir
   )
 
+  install_data('net.zoite.Zoitechat.mime.xml',
+    install_dir: mimedir
+  )
+
   if desktop_utils.found()
     test('Validate net.zoite.Zoitechat.desktop', desktop_utils,
       args: [zoitechat_desktop]
diff --git a/data/misc/net.zoite.Zoitechat.desktop.in.in b/data/misc/net.zoite.Zoitechat.desktop.in.in
index d2c3d36b..26efc8f6 100644
--- a/data/misc/net.zoite.Zoitechat.desktop.in.in
+++ b/data/misc/net.zoite.Zoitechat.desktop.in.in
@@ -11,7 +11,7 @@ Categories=GTK;Network;IRCClient;
 StartupNotify=true
 StartupWMClass=Zoitechat
 X-GNOME-UsesNotifications=true
-MimeType=x-scheme-handler/irc;x-scheme-handler/ircs;
+MimeType=x-scheme-handler/irc;x-scheme-handler/ircs;application/x-zoitechat-theme;application/x-hexchat-theme;
 Actions=SafeMode;
 
 [Desktop Action SafeMode]
diff --git a/data/misc/net.zoite.Zoitechat.mime.xml b/data/misc/net.zoite.Zoitechat.mime.xml
new file mode 100644
index 00000000..a262c9c2
--- /dev/null
+++ b/data/misc/net.zoite.Zoitechat.mime.xml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
+  <mime-type type="application/x-zoitechat-theme">
+    <comment>ZoiteChat Theme</comment>
+    <glob pattern="*.zct"/>
+  </mime-type>
+  <mime-type type="application/x-hexchat-theme">
+    <comment>HexChat Theme</comment>
+    <glob pattern="*.hct"/>
+  </mime-type>
+</mime-info>
diff --git a/osx/Info.plist.in b/osx/Info.plist.in
index 2b732447..073886eb 100644
--- a/osx/Info.plist.in
+++ b/osx/Info.plist.in
@@ -22,6 +22,22 @@
     <string>????</string>
     <key>CFBundleVersion</key>
     <string>@VERSION@</string>
+    <key>CFBundleDocumentTypes</key>
+    <array>
+        <dict>
+            <key>CFBundleTypeExtensions</key>
+            <array>
+                <string>zct</string>
+                <string>hct</string>
+            </array>
+            <key>CFBundleTypeIconFile</key>
+            <string>zoitechat.icns</string>
+            <key>CFBundleTypeName</key>
+            <string>ZoiteChat Theme</string>
+            <key>CFBundleTypeRole</key>
+            <string>Viewer</string>
+        </dict>
+    </array>
     <key>NSHumanReadableCopyright</key>
     <string></string>
     <key>LSMinimumSystemVersion</key>
diff --git a/win32/installer/zoitechat-arm64.iss b/win32/installer/zoitechat-arm64.iss
index eaf4feda..b32c4239 100644
--- a/win32/installer/zoitechat-arm64.iss
+++ b/win32/installer/zoitechat-arm64.iss
@@ -99,6 +99,11 @@ Root: HKCR; Subkey: "irc"; ValueType: string; ValueName: "URL Protocol"; ValueDa
 Root: HKCR; Subkey: "irc\DefaultIcon"; ValueType: string; ValueName: ""; ValueData: "{app}\zoitechat.exe,0"; Flags: uninsdeletevalue; Tasks: not portable
 Root: HKCR; Subkey: "irc\shell"; ValueType: string; ValueName: ""; ValueData: "open"; Flags: uninsdeletevalue; Tasks: not portable
 Root: HKCR; Subkey: "irc\shell\open\command"; ValueType: string; ValueName: ""; ValueData: "{app}\zoitechat.exe --url=""%1"""; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: ".zct"; ValueType: string; ValueName: ""; ValueData: "ZoiteChat.Theme"; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: ".hct"; ValueType: string; ValueName: ""; ValueData: "ZoiteChat.Theme"; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: "ZoiteChat.Theme"; ValueType: string; ValueName: ""; ValueData: "ZoiteChat Theme"; Flags: uninsdeletekey; Tasks: not portable
+Root: HKCR; Subkey: "ZoiteChat.Theme\DefaultIcon"; ValueType: string; ValueName: ""; ValueData: "{app}\zoitechat.exe,0"; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: "ZoiteChat.Theme\shell\open\command"; ValueType: string; ValueName: ""; ValueData: """{app}\zoitechat.exe"" ""%1"""; Flags: uninsdeletevalue; Tasks: not portable
 
 [Run]
 Filename: "{app}\zoitechat.exe"; Description: "Run ZoiteChat after closing the Wizard"; Flags: nowait postinstall skipifsilent
diff --git a/win32/installer/zoitechat.iss.tt b/win32/installer/zoitechat.iss.tt
index 758059b4..14de669c 100644
--- a/win32/installer/zoitechat.iss.tt
+++ b/win32/installer/zoitechat.iss.tt
@@ -86,6 +86,11 @@ Root: HKCR; Subkey: "irc"; ValueType: string; ValueName: "URL Protocol"; ValueDa
 Root: HKCR; Subkey: "irc\DefaultIcon"; ValueType: string; ValueName: ""; ValueData: "{app}\zoitechat.exe,0"; Flags: uninsdeletevalue; Tasks: not portable
 Root: HKCR; Subkey: "irc\shell"; ValueType: string; ValueName: ""; ValueData: "open"; Flags: uninsdeletevalue; Tasks: not portable
 Root: HKCR; Subkey: "irc\shell\open\command"; ValueType: string; ValueName: ""; ValueData: "{app}\zoitechat.exe --url=""%1"""; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: ".zct"; ValueType: string; ValueName: ""; ValueData: "ZoiteChat.Theme"; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: ".hct"; ValueType: string; ValueName: ""; ValueData: "ZoiteChat.Theme"; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: "ZoiteChat.Theme"; ValueType: string; ValueName: ""; ValueData: "ZoiteChat Theme"; Flags: uninsdeletekey; Tasks: not portable
+Root: HKCR; Subkey: "ZoiteChat.Theme\DefaultIcon"; ValueType: string; ValueName: ""; ValueData: "{app}\zoitechat.exe,0"; Flags: uninsdeletevalue; Tasks: not portable
+Root: HKCR; Subkey: "ZoiteChat.Theme\shell\open\command"; ValueType: string; ValueName: ""; ValueData: """{app}\zoitechat.exe"" ""%1"""; Flags: uninsdeletevalue; Tasks: not portable
 
 [Run]
 Filename: "{app}\zoitechat.exe"; Description: "Run ZoiteChat after closing the Wizard"; Flags: nowait postinstall skipifsilent