diff --git a/packages/gatsby-plugin-page-creator/src/gatsby-node.ts b/packages/gatsby-plugin-page-creator/src/gatsby-node.ts
index 6dff9f2f6e168..7ffe6b65a8a2f 100644
--- a/packages/gatsby-plugin-page-creator/src/gatsby-node.ts
+++ b/packages/gatsby-plugin-page-creator/src/gatsby-node.ts
@@ -190,11 +190,13 @@ Please pick a path to an existing directory.`,
 
       const hasTrailingSlash = derivedPath.endsWith(`/`)
       const path = createPath(derivedPath, hasTrailingSlash, true)
+      const modifiedPath = applyTrailingSlashOption(path, trailingSlash)
+
       // We've already created a page with this path
-      if (this.knownPagePaths.has(path)) {
+      if (this.knownPagePaths.has(modifiedPath)) {
         return undefined
       }
-      this.knownPagePaths.add(path)
+      this.knownPagePaths.add(modifiedPath)
       // Params is supplied to the FE component on props.params
       const params = getCollectionRouteParams(createPath(filePath), path)
       // nodeParams is fed to the graphql query for the component
@@ -202,8 +204,6 @@ Please pick a path to an existing directory.`,
       // matchPath is an optional value. It's used if someone does a path like `{foo}/[bar].js`
       const matchPath = getMatchPath(path)
 
-      const modifiedPath = applyTrailingSlashOption(path, trailingSlash)
-
       const componentPath = contentFilePath
         ? `${absolutePath}?__contentFilePath=${contentFilePath}`
         : absolutePath