diff --git a/material-ui/index.d.ts b/material-ui/index.d.ts
index 941b7aff72..c04d673dc9 100644
--- a/material-ui/index.d.ts
+++ b/material-ui/index.d.ts
@@ -141,7 +141,7 @@ declare namespace __MaterialUI {
             fontFamily?: string;
             palette?: ThemePalette;
             isRtl?: boolean;
-            userAgent?: string;
+            userAgent?: string | boolean;
             zIndex?: zIndex;
             baseTheme?: RawTheme;
             rawTheme?: RawTheme;