diff --git a/docs/changes.txt b/docs/changes.txt
index 268da62bc7..65f2e34b99 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -272,6 +272,7 @@ wxMSW
 
 wxOSX:
 
+- Fix crash on startup when using Farsi as system language (#25561).
 - Do not activate "Close" button on Cmd-C (nobugshere, #25346).
 
 
diff --git a/src/osx/carbon/app.cpp b/src/osx/carbon/app.cpp
index c5c7596a46..e5ce0db58b 100644
--- a/src/osx/carbon/app.cpp
+++ b/src/osx/carbon/app.cpp
@@ -306,7 +306,12 @@ bool wxApp::Initialize(int& argc, wxChar **argv)
         return false;
 
 #if wxUSE_INTL
-    wxFont::SetDefaultEncoding(wxLocale::GetSystemEncoding());
+    // Check if we recognize the system encoding. Note that we must not call
+    // SetDefaultEncoding() if we don't, as indicated by wxFONTENCODING_DEFAULT
+    // being returned, as SetDefaultEncoding() would assert in this case.
+    const wxFontEncoding defaultEncoding = wxLocale::GetSystemEncoding();
+    if ( defaultEncoding != wxFONTENCODING_DEFAULT )
+        wxFont::SetDefaultEncoding(defaultEncoding);
 #endif
 
     // these might be the startup dirs, set them to the 'usual' dir containing the app bundle