diff --git a/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-a.js b/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-a.js
new file mode 100644
index 0000000000000..3884c811330aa
--- /dev/null
+++ b/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-a.js
@@ -0,0 +1 @@
+module.exports = "file-a from theme-a";
diff --git a/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-b.customscript b/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-b.customscript
new file mode 100644
index 0000000000000..e5b35571fee15
--- /dev/null
+++ b/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-b.customscript
@@ -0,0 +1 @@
+module.exports = "file-b from theme-a";
diff --git a/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-c.js b/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-c.js
new file mode 100644
index 0000000000000..3884c811330aa
--- /dev/null
+++ b/packages/gatsby/src/internal-plugins/webpack-theme-component-shadowing/__tests__/fixtures/test-sites/legacy-extensions-shadowing/node_modules/theme-a/src/file-c.js
@@ -0,0 +1 @@
+module.exports = "file-a from theme-a";