diff --git a/packages/mui-material/src/Stack/Stack.test.js b/packages/mui-material/src/Stack/Stack.test.js
index affeadb68f2f02..66f14c88d8c838 100644
--- a/packages/mui-material/src/Stack/Stack.test.js
+++ b/packages/mui-material/src/Stack/Stack.test.js
@@ -298,6 +298,7 @@ describe('<Stack />', () => {
           },
         },
         display: 'flex',
+        flexDirection: 'column',
       });
 
       expect(
@@ -342,6 +343,7 @@ describe('<Stack />', () => {
           },
         },
         display: 'flex',
+        flexDirection: 'column',
       });
     });
   });