diff --git a/packages/client/src/scripts/katex-macro.ts b/packages/client/src/scripts/katex-macro.ts
index 4368095be4..4c176b2962 100644
--- a/packages/client/src/scripts/katex-macro.ts
+++ b/packages/client/src/scripts/katex-macro.ts
@@ -264,6 +264,8 @@ function expandKaTeXMacroOnce(
 			}
 		}
 
+		if (!macros.hasOwnProperty(macroName)) return [fallback, false];
+
 		const numArgs: number = macros[macroName].args;
 		const openBracket: string = macroName.slice(-1);