diff --git a/config/hypr/hyprland.lua b/config/hypr/hyprland.lua
index 613d5ca..7c8b7d8 100644
--- a/config/hypr/hyprland.lua
+++ b/config/hypr/hyprland.lua
@@ -19,7 +19,9 @@ hl.monitor({
 -- ── Environment Variables ──
 hl.env("XCURSOR_SIZE", "24")
 hl.env("XCURSOR_THEME", "Colloid-cursors")
-hl.env("QT_QPA_PLATFORM", "wayland")
+-- xcb is the fallback for a Qt app whose wayland plugin is not installed
+-- (qt5-wayland for Qt5): with "wayland" alone Qt aborts instead.
+hl.env("QT_QPA_PLATFORM", "wayland;xcb")
 -- qt5ct is a Qt5-only platform theme plugin: Qt6 apps (Quickshell, and so
 -- Noctalia) never load it and end up on "hicolor" for icons. Noctalia's icon
 -- theme is therefore pinned separately via QS_ICON_THEME in scripts/stoa-bar.sh,
diff --git a/config/niri/config.kdl b/config/niri/config.kdl
index 3b210df..715f0a8 100644
--- a/config/niri/config.kdl
+++ b/config/niri/config.kdl
@@ -50,7 +50,9 @@ input {
 // niri-session already exports XDG_CURRENT_DESKTOP=niri and
 // XDG_SESSION_TYPE=wayland, so only the toolkit and theme variables go here.
 environment {
-    QT_QPA_PLATFORM "wayland"
+    // xcb (through xwayland-satellite) is the fallback for a Qt app whose
+    // wayland plugin is not installed: with "wayland" alone Qt aborts.
+    QT_QPA_PLATFORM "wayland;xcb"
     // qt5ct is Qt5-only; Noctalia (Qt6) gets its icon theme from
     // scripts/stoa-bar.sh — see the same note in hyprland.lua.
     QT_QPA_PLATFORMTHEME "qt5ct"
diff --git a/setup/post-install.sh b/setup/post-install.sh
index bad4a8e..c498473 100755
--- a/setup/post-install.sh
+++ b/setup/post-install.sh
@@ -177,8 +177,10 @@ SHELL_PKGS_QS="noctalia"
 # Fonts and theme
 FONT_PKGS="ttf-jetbrains-mono ttf-font-awesome"
 
-# Toolkit unification (Qt = GTK appearance)
-THEME_PKGS="qt5ct qt6ct"
+# Toolkit unification (Qt = GTK appearance). qt5-wayland/qt6-wayland are
+# the Qt platform plugins for a Wayland session; without qt5-wayland a
+# Qt5 app (bauh, via PyQt5) aborts on start under QT_QPA_PLATFORM=wayland.
+THEME_PKGS="qt5ct qt6ct qt5-wayland qt6-wayland"
 
 # Firewall
 FIREWALL_PKGS="nftables"