diff --git a/packages/typescript-estree/src/create-program/shared.ts b/packages/typescript-estree/src/create-program/shared.ts
index a436ec7082d8..ac2dc3d5e62e 100644
--- a/packages/typescript-estree/src/create-program/shared.ts
+++ b/packages/typescript-estree/src/create-program/shared.ts
@@ -21,8 +21,10 @@ const DEFAULT_COMPILER_OPTIONS: ts.CompilerOptions = {
 // This narrows the type so we can be sure we're passing canonical names in the correct places
 type CanonicalPath = string & { __brand: unknown };
 const getCanonicalFileName = ts.sys.useCaseSensitiveFileNames
-  ? (path: string): CanonicalPath => path as CanonicalPath
-  : (path: string): CanonicalPath => path.toLowerCase() as CanonicalPath;
+  ? (filePath: string): CanonicalPath =>
+      path.normalize(filePath) as CanonicalPath
+  : (filePath: string): CanonicalPath =>
+      path.normalize(filePath).toLowerCase() as CanonicalPath;
 
 function getTsconfigPath(tsconfigPath: string, extra: Extra): CanonicalPath {
   return getCanonicalFileName(