diff --git a/apps/web/src/terminal/ghostty/surface.ts b/apps/web/src/terminal/ghostty/surface.ts
index 8dee6218fb916f0b977a3c2ab0c4afd6bece72b6..fc7a89c6d31ee1ef7298f00c73cdb00cae1cffec 100644
--- a/apps/web/src/terminal/ghostty/surface.ts
+++ b/apps/web/src/terminal/ghostty/surface.ts
@@ -604,6 +604,11 @@ export class GhosttyTerminalSurface {
 
     const context = canvas.getContext("2d", { alpha: false });
     if (!context) throw new Error("Canvas 2D is unavailable");
+    // An opaque canvas backing store initializes to solid black, and the font
+    // and WASM loads below leave it on screen for the whole setup window; paint
+    // the theme background first so the mount never flashes a black box.
+    context.fillStyle = `rgb(${options.theme.background.r}, ${options.theme.background.g}, ${options.theme.background.b})`;
+    context.fillRect(0, 0, canvas.width, canvas.height);
     const fontSize = terminalFontSize(options.font?.size);
     try {
       // Cell metrics must come from the faces that will render; measuring before