diff --git a/src/lib/types/auth_forms.ts b/src/lib/types/auth_forms.ts
index 7cecc61fc..7fde5e132 100644
--- a/src/lib/types/auth_forms.ts
+++ b/src/lib/types/auth_forms.ts
@@ -19,7 +19,9 @@ export type AuthFormConstraints = {
   password?: FieldConstraints;
 };
 
-type SchemaShape = Record<string, unknown>;
+// Must match the recursive SchemaShape from sveltekit-superforms (dist/jsonSchema/schemaShape.d.ts)
+// Record<string, SchemaShape> is semantically equivalent but triggers TS circular reference error.
+type SchemaShape = { [K in string]: SchemaShape };
 
 /**
  * Represents the state and data structure for authentication forms.
diff --git a/src/lib/utils/auth_forms.ts b/src/lib/utils/auth_forms.ts
index 3e387b3f4..186b86f6e 100644
--- a/src/lib/utils/auth_forms.ts
+++ b/src/lib/utils/auth_forms.ts
@@ -164,9 +164,11 @@ const createBaseAuthForm = () => ({
       pattern: '(?=.*?[a-z])(?=.*?[A-Z])(?=.*?\\d)[a-zA-Z\\d]{8,128}',
     },
   },
+  // Primitive fields get empty objects; only arrays/objects produce nested shape nodes.
+  // See: sveltekit-superforms/src/lib/jsonSchema/schemaShape.ts (_schemaShape)
   shape: {
-    username: { type: 'string' },
-    password: { type: 'string' },
+    username: {},
+    password: {},
   },
 });
 
diff --git a/src/test/lib/utils/auth_forms.test.ts b/src/test/lib/utils/auth_forms.test.ts
index 2309d9fbd..1cc277acf 100644
--- a/src/test/lib/utils/auth_forms.test.ts
+++ b/src/test/lib/utils/auth_forms.test.ts
@@ -27,8 +27,8 @@ vi.mock('$lib/zod/schema', () => ({
   authSchema: {
     _type: 'ZodObject',
     shape: {
-      username: { type: 'string' },
-      password: { type: 'string' },
+      username: {},
+      password: {},
     },
   },
 }));
@@ -129,8 +129,8 @@ describe('auth_forms', () => {
           },
         },
         shape: {
-          username: { type: 'string' },
-          password: { type: 'string' },
+          username: {},
+          password: {},
         } as unknown,
         message: '',
       } as unknown as SuperValidated<Record<string, string>, string>;
@@ -205,8 +205,8 @@ describe('auth_forms', () => {
 
       expect(result.form.shape).toBeDefined();
       expect(result.form.shape).toEqual({
-        username: { type: 'string' },
-        password: { type: 'string' },
+        username: {},
+        password: {},
       });
     });