diff --git a/modules/misc/gtk.nix b/modules/misc/gtk.nix
index 2409376cb6e6..99e0bfddf44e 100644
--- a/modules/misc/gtk.nix
+++ b/modules/misc/gtk.nix
@@ -59,7 +59,7 @@ in
     theme = mkOption {
       type = types.nullOr themeType;
       default = null;
-      description = "Default theme for all GTK versions.";
+      description = "Default theme for GTK 2/3.";
     };
 
     iconTheme = mkOption {
diff --git a/modules/misc/gtk/gtk4.nix b/modules/misc/gtk/gtk4.nix
index 7e5c4f0bc9d3..e140c2689d32 100644
--- a/modules/misc/gtk/gtk4.nix
+++ b/modules/misc/gtk/gtk4.nix
@@ -45,9 +45,12 @@ in
           packageExample = "pkgs.gnome.gnome-themes-extra";
         }
       );
-      default = cfg.theme;
-      defaultText = literalExpression "config.gtk.theme";
-      description = "Theme for GTK 4 applications.";
+      default = null;
+      description = ''
+        Theme for GTK 4 applications.
+
+        Warning: This is not officially supported and applied using a workaround, and may cause issues.
+      '';
     };
 
     iconTheme = mkOption {
diff --git a/modules/misc/news/2025/09/2025-09-17_12-26-31.nix b/modules/misc/news/2025/09/2025-09-17_12-26-31.nix
new file mode 100644
index 000000000000..b859bd010f64
--- /dev/null
+++ b/modules/misc/news/2025/09/2025-09-17_12-26-31.nix
@@ -0,0 +1,10 @@
+{
+  time = "2025-09-17T10:26:31+00:00";
+  condition = true;
+  message = ''
+    The option 'gtk.theme' does not apply to GTK 4 automatically anymore. Using a
+    custom theme is not officially supported by GTK 4, and is implemented by
+    home-manager using a workaround that may cause issues in some cases. If you
+    still want to use a GTK 4 theme, you need to explicitly set 'gtk.gtk4.theme'.
+  '';
+}
diff --git a/tests/modules/misc/gtk/gtk-global-inheritance-gtk4-css-expected.css b/tests/modules/misc/gtk/gtk-global-inheritance-gtk4-css-expected.css
deleted file mode 100644
index a8f04a5ca3f8..000000000000
--- a/tests/modules/misc/gtk/gtk-global-inheritance-gtk4-css-expected.css
+++ /dev/null
@@ -1,5 +0,0 @@
-/**
- * GTK 4 reads the theme configured by gtk-theme-name, but ignores it.
- * It does however respect user CSS, so import the theme from here.
-**/
-@import url("file://@gnome-themes-extra@/share/themes/Adwaita-dark/gtk-4.0/gtk.css");
diff --git a/tests/modules/misc/gtk/gtk-global-inheritance-gtk4-expected.ini b/tests/modules/misc/gtk/gtk-global-inheritance-gtk4-expected.ini
index 8e08f8d5d2be..68697d618fce 100644
--- a/tests/modules/misc/gtk/gtk-global-inheritance-gtk4-expected.ini
+++ b/tests/modules/misc/gtk/gtk-global-inheritance-gtk4-expected.ini
@@ -5,4 +5,3 @@ gtk-cursor-theme-size=24
 gtk-font-name=Ubuntu 12
 gtk-icon-theme-name=Adwaita
 gtk-interface-color-scheme=2
-gtk-theme-name=Adwaita-dark
diff --git a/tests/modules/misc/gtk/gtk-global-inheritance.nix b/tests/modules/misc/gtk/gtk-global-inheritance.nix
index 3d01f4843963..bcb73007a153 100644
--- a/tests/modules/misc/gtk/gtk-global-inheritance.nix
+++ b/tests/modules/misc/gtk/gtk-global-inheritance.nix
@@ -37,9 +37,5 @@
     assertFileExists home-files/.config/gtk-4.0/settings.ini
     assertFileContent home-files/.config/gtk-4.0/settings.ini \
       ${./gtk-global-inheritance-gtk4-expected.ini}
-
-    # Check GTK4 CSS with theme import
-    assertFileExists home-files/.config/gtk-4.0/gtk.css
-    assertFileContent home-files/.config/gtk-4.0/gtk.css ${./gtk-global-inheritance-gtk4-css-expected.css}
   '';
 }
diff --git a/tests/modules/misc/gtk/gtk-per-version-override-gtk4-expected.ini b/tests/modules/misc/gtk/gtk-per-version-override-gtk4-expected.ini
index 25b6ea043061..33c58e970156 100644
--- a/tests/modules/misc/gtk/gtk-per-version-override-gtk4-expected.ini
+++ b/tests/modules/misc/gtk/gtk-per-version-override-gtk4-expected.ini
@@ -3,4 +3,3 @@ gtk-cursor-theme-name=Global-Cursor
 gtk-font-name=GTK4-Font 11
 gtk-icon-theme-name=Global-Icons
 gtk-recent-files-limit=20
-gtk-theme-name=Global-Theme
diff --git a/tests/modules/misc/gtk/gtk-per-version-override.nix b/tests/modules/misc/gtk/gtk-per-version-override.nix
index 0273de70949c..4881f86e1948 100644
--- a/tests/modules/misc/gtk/gtk-per-version-override.nix
+++ b/tests/modules/misc/gtk/gtk-per-version-override.nix
@@ -46,7 +46,7 @@
     assertFileContent home-files/.config/gtk-3.0/gtk.css \
       ${./gtk-per-version-override-gtk3-css-expected.css}
 
-    # GTK4 should use overridden font, global theme/icons/cursor
+    # GTK4 should use overridden font, global icons/cursor
     assertFileExists home-files/.config/gtk-4.0/settings.ini
     assertFileContent home-files/.config/gtk-4.0/settings.ini \
       ${./gtk-per-version-override-gtk4-expected.ini}
diff --git a/tests/modules/misc/gtk/gtk4/gtk4-basic-settings.nix b/tests/modules/misc/gtk/gtk4/gtk4-basic-settings.nix
index 101cb0258564..874ce09afc56 100644
--- a/tests/modules/misc/gtk/gtk4/gtk4-basic-settings.nix
+++ b/tests/modules/misc/gtk/gtk4/gtk4-basic-settings.nix
@@ -2,11 +2,11 @@
 {
   gtk = {
     enable = true;
-    theme = {
-      name = "catppuccin-macchiato-blue-standard";
-      package = pkgs.catppuccin-gtk;
-    };
     gtk4 = {
+      theme = {
+        name = "catppuccin-macchiato-blue-standard";
+        package = pkgs.catppuccin-gtk;
+      };
       extraConfig = {
         gtk-cursor-blink = false;
         gtk-recent-files-limit = 20;