--- a/dom/media/MediaPrefs.h
+++ b/dom/media/MediaPrefs.h
@@ -189,19 +189,24 @@ private:
   DECL_MEDIA_PREF("media.flac.enabled",                       FlacEnabled, bool, true);
 
   // Hls
   DECL_MEDIA_PREF("media.hls.enabled",                        HLSEnabled, bool, false);
 
   // Both rust/stagefright will be enabled when this is true regardless of 'media.rust.mp4parser'.
   DECL_MEDIA_PREF("media.rust.test_mode",                     RustTestMode, bool, false);
 
+#if defined(XP_WIN) && !defined(_WIN64)
+  // Disable rust parser for win32 due to bug 1389470.
+  DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, false);
+#else
   // True, it enables rust parser and fallback to stagefright if rust parser fails.
   // False, it uses stagefright only.
   DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, true);
+#endif
 
   DECL_MEDIA_PREF("media.mp4.enabled",                        MP4Enabled, bool, false);
 
   // Error/warning handling, Decoder Doctor
   DECL_MEDIA_PREF("media.playback.warnings-as-errors",        MediaWarningsAsErrors, bool, false);
   DECL_MEDIA_PREF("media.playback.warnings-as-errors.stagefright-vs-rust",
                                                               MediaWarningsAsErrorsStageFrightVsRust, bool, false);