diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 27f9f98d71..beb7b6f642 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -116,7 +116,7 @@ jobs:
       - name: Setup Meson
         run: |
           python -m pip install --upgrade pip setuptools
-          pip install meson
+          pip install meson==1.4.2
 
       - name: Setup MSVC
         if: matrix.config.os == 'windows-latest' && matrix.config.msvc == true
diff --git a/automation/vapoursynth/aegisub_vs.py b/automation/vapoursynth/aegisub_vs.py
index 7de104ddcb..ef610b4033 100644
--- a/automation/vapoursynth/aegisub_vs.py
+++ b/automation/vapoursynth/aegisub_vs.py
@@ -195,7 +195,8 @@ def wrap_lwlibavsource(filename: str, cachedir: str | None = None, **kwargs: Any
 
     ensure_plugin("lsmas", "libvslsmashsource", "To use Aegisub's LWLibavSource wrapper, the `lsmas` plugin for VapourSynth must be installed")
 
-    if b"-Dcachedir" not in core.lsmas.Version()["config"]: # type: ignore
+    import inspect
+    if "cachedir" not in inspect.getfullargspec(vs.core.lsmas.LWLibavSource).args:
         raise vs.Error("To use Aegisub's LWLibavSource wrapper, the `lsmas` plugin must support the `cachedir` option for LWLibavSource.")
 
     clip = core.lsmas.LWLibavSource(source=filename, cachefile=cachefile, **kwargs)