diff --git a/packages/mui-material/src/styles/createTheme.spec.ts b/packages/mui-material/src/styles/createTheme.spec.ts
index 0e99ba47cfd7de..f86a12a414f759 100644
--- a/packages/mui-material/src/styles/createTheme.spec.ts
+++ b/packages/mui-material/src/styles/createTheme.spec.ts
@@ -182,3 +182,12 @@ const theme = createTheme();
     },
   });
 }
+
+{
+  createTheme({
+    shape: {
+      // @ts-expect-error invalid borderRadius string value in theme
+      borderRadius: '5px',
+    },
+  });
+}
diff --git a/packages/mui-system/src/createTheme/shape.d.ts b/packages/mui-system/src/createTheme/shape.d.ts
index 073fb7b94c50b0..fba5ed44f378a0 100644
--- a/packages/mui-system/src/createTheme/shape.d.ts
+++ b/packages/mui-system/src/createTheme/shape.d.ts
@@ -1,5 +1,5 @@
 export interface Shape {
-  borderRadius: number | string;
+  borderRadius: number;
 }
 
 export type ShapeOptions = Partial<Shape>;