diff --git a/.changeset/swingset-stylex-include.md b/.changeset/swingset-stylex-include.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/swingset-stylex-include.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/packages/swingset/postcss.config.mjs b/packages/swingset/postcss.config.mjs
index 3466a51d4a4..7bc3bc16552 100644
--- a/packages/swingset/postcss.config.mjs
+++ b/packages/swingset/postcss.config.mjs
@@ -23,6 +23,7 @@ const isDev = process.env.NODE_ENV !== 'production';
 // defaults never change mid-session, so they stay correct.
 const stylexExtraction = {
   '@stylexjs/postcss-plugin': {
+    include: [resolve(__dirname, 'src/**/*.{ts,tsx}'), resolve(mosaicRoot, 'src/**/*.{ts,tsx}')],
     useCSSLayers: true,
     babelConfig: {
       babelrc: false,