diff --git a/theme/beamerfontthemeOUCSlide.sty b/theme/beamerfontthemeOUCSlide.sty
index 18652ea..44f5c2f 100644
--- a/theme/beamerfontthemeOUCSlide.sty
+++ b/theme/beamerfontthemeOUCSlide.sty
@@ -206,37 +206,38 @@
     {}%
     {\PackageError{beameroucslide}{Patching original part failed}\@ehc}
 % beamer 3.69（TeX Live 2023）起 \beamer@@frametitle 的定义发生了变化：
-%   1. 内部增加了 \ifblank 判断；
-%   2. 用 \beamer@insertframetitlecontinuation 取代了 \usebeamertemplate*{frametitle continuation}。
+%   用 \beamer@insertframetitlecontinuation 取代了 \usebeamertemplate*{frametitle continuation}。
 % 因此这里按 beamer 版本分别处理，保证在 TeX Live 2022 与 2023 下都能编译通过。
-\@ifundefined{beamer@insertframetitlecontinuation}
-    {% 旧版 beamer（TeX Live 2022 及以前）：沿用原有的补丁方式
-        \patchcmd{\beamer@@frametitle}
-            {{%
-                \gdef\insertframetitle{{#2\ifnum\beamer@autobreakcount>0\relax{}\space%
-                \usebeamertemplate*{frametitle continuation}\fi}}%
-                \gdef\beamer@frametitle{#2}%
-                \gdef\beamer@shortframetitle{#1}%
-            }}
-            {{%
-                \gdef\insertframetitle{{\beameroucslide@frametitleformatcaps{#2}\ifnum%
-                \beamer@autobreakcount>0\relax{}\space%
-                \usebeamertemplate*{frametitle continuation}\fi}}%
-                \gdef\beamer@frametitle{#2}%
-                \gdef\beamer@shortframetitle{#1}%
-            }}
-            {}
-            {\PackageError{beameroucslide}{Patching original frame title failed}\@ehc}%
-    }
-    {% 新版 beamer（TeX Live 2023 及以后）：按新定义重写，并加入标题格式控制
-        \long\def\beamer@@frametitle[#1]#2{%
-            \ifblank{#2}{}{%
-                \gdef\insertframetitle{{\beameroucslide@frametitleformatcaps{#2}%
-                    \ifnum\beamer@autobreakcount>0\relax{}\space%
-                    \beamer@insertframetitlecontinuation\fi}}%
-                \gdef\beamer@frametitle{#2}%
-                \gdef\beamer@shortframetitle{#1}%
-            }%
+% 注意：判断必须写在文件顶层（不能把 \patchcmd 嵌进 \@ifundefined 等宏的参数里），
+% 否则 \patchcmd 的搜索串会被改写而导致补丁失败。
+\ifcsname beamer@insertframetitlecontinuation\endcsname
+    % 新版 beamer（TeX Live 2023 及以后）：按新定义重写，并加入标题格式控制
+    \long\def\beamer@@frametitle[#1]#2{%
+        \ifblank{#2}{}{%
+            \gdef\insertframetitle{{\beameroucslide@frametitleformatcaps{#2}%
+                \ifnum\beamer@autobreakcount>0\relax{}\space%
+                \beamer@insertframetitlecontinuation\fi}}%
+            \gdef\beamer@frametitle{#2}%
+            \gdef\beamer@shortframetitle{#1}%
         }%
-    }
+    }%
+\else
+    % 旧版 beamer（TeX Live 2022 及以前）：沿用原有的补丁方式
+    \patchcmd{\beamer@@frametitle}
+        {{%
+            \gdef\insertframetitle{{#2\ifnum\beamer@autobreakcount>0\relax{}\space%
+            \usebeamertemplate*{frametitle continuation}\fi}}%
+            \gdef\beamer@frametitle{#2}%
+            \gdef\beamer@shortframetitle{#1}%
+        }}
+        {{%
+            \gdef\insertframetitle{{\beameroucslide@frametitleformatcaps{#2}\ifnum%
+            \beamer@autobreakcount>0\relax{}\space%
+            \usebeamertemplate*{frametitle continuation}\fi}}%
+            \gdef\beamer@frametitle{#2}%
+            \gdef\beamer@shortframetitle{#1}%
+        }}
+        {}
+        {\PackageError{beameroucslide}{Patching original frame title failed}\@ehc}%
+\fi
 \makeatother