diff --git a/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs b/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs
index 3c297f7b..fcf50b42 100644
--- a/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs
+++ b/crates/fbuild-build-mcu/src/ch32v/orchestrator.rs
@@ -132,9 +132,6 @@ impl BuildOrchestrator for Ch32vOrchestrator {
         if let Some(vh) = resolve_variant_h(&variant_dir, ctx.board.variant_h.as_deref()) {
             defines.insert("VARIANT_H".to_string(), format!("\\\"{}\\\"", vh));
         }
-        if series == "ch32x035" {
-            defines.insert("RCC_BackupResetCmd(x)".to_string(), "((void)0)".to_string());
-        }
         // Use resolved core_dir/variant_dir directly — board.get_include_paths()
         // uses the raw board core name which may differ from the actual directory
         // (e.g. OpenWCH core dir is "arduino", not "openwch").
diff --git a/crates/fbuild-library/src/library/ch32v_core.rs b/crates/fbuild-library/src/library/ch32v_core.rs
index b034e041..3383a56f 100644
--- a/crates/fbuild-library/src/library/ch32v_core.rs
+++ b/crates/fbuild-library/src/library/ch32v_core.rs
@@ -91,11 +91,6 @@ impl Ch32vCores {
         Ok(())
     }
 
-    /// Apply compatibility patches for known upstream core issues.
-    fn patch_compatibility(root: &Path) -> fbuild_core::Result<()> {
-        patch_backup_header(root)
-    }
-
     /// Get the core source directory for a specific core name.
     ///
     /// The board JSON `core` field (e.g. "openwch") comes from PlatformIO's
@@ -136,14 +131,12 @@ impl crate::Package for Ch32vCores {
     async fn ensure_installed(&self) -> fbuild_core::Result<PathBuf> {
         if self.is_installed() {
             let root = self.resolved_dir();
-            Self::patch_compatibility(&root)?;
             return Ok(root);
         }
 
         let install_path = self.base.staged_install(Self::validate).await?;
 
         let root = find_core_root(&install_path);
-        Self::patch_compatibility(&root)?;
         Ok(root)
     }
 
@@ -194,39 +187,6 @@ fn find_core_root(install_dir: &Path) -> PathBuf {
     install_dir.to_path_buf()
 }
 
-fn patch_backup_header(root: &Path) -> fbuild_core::Result<()> {
-    let backup_h = root
-        .join("cores")
-        .join("arduino")
-        .join("ch32")
-        .join("backup.h");
-    if !backup_h.exists() {
-        return Ok(());
-    }
-
-    let content = std::fs::read_to_string(&backup_h).map_err(|e| {
-        fbuild_core::FbuildError::PackageError(format!(
-            "failed to read CH32V backup header {}: {}",
-            backup_h.display(),
-            e
-        ))
-    })?;
-
-    let patched = content.replace("#ifndef CH32V00x", "#ifdef RCC_APB1Periph_BKP");
-    if patched != content {
-        std::fs::write(&backup_h, patched).map_err(|e| {
-            fbuild_core::FbuildError::PackageError(format!(
-                "failed to patch CH32V backup header {}: {}",
-                backup_h.display(),
-                e
-            ))
-        })?;
-        tracing::debug!("patched {}", backup_h.display());
-    }
-
-    Ok(())
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -261,27 +221,4 @@ mod tests {
         assert!(result.is_err());
     }
 
-    #[test]
-    fn test_patch_backup_header_replaces_old_guard() {
-        let tmp = tempfile::TempDir::new().unwrap();
-        let backup_h = tmp.path().join("cores/arduino/ch32/backup.h");
-        std::fs::create_dir_all(backup_h.parent().unwrap()).unwrap();
-        std::fs::write(
-            &backup_h,
-            "static inline void resetBackupDomain(void)\n{\n#ifndef CH32V00x\n  RCC_BackupResetCmd(ENABLE);\n  RCC_BackupResetCmd(DISABLE);\n#endif\n}\n",
-        )
-        .unwrap();
-
-        patch_backup_header(tmp.path()).unwrap();
-
-        let patched = std::fs::read_to_string(&backup_h).unwrap();
-        assert!(patched.contains("#ifdef RCC_APB1Periph_BKP"));
-        assert!(!patched.contains("#ifndef CH32V00x"));
-    }
-
-    #[test]
-    fn test_patch_backup_header_is_noop_when_missing() {
-        let tmp = tempfile::TempDir::new().unwrap();
-        patch_backup_header(tmp.path()).unwrap();
-    }
 }