diff --git a/crates/oxc_codegen/src/sourcemap_builder.rs b/crates/oxc_codegen/src/sourcemap_builder.rs
index 597aafb75..c5c091821 100644
--- a/crates/oxc_codegen/src/sourcemap_builder.rs
+++ b/crates/oxc_codegen/src/sourcemap_builder.rs
@@ -62,12 +62,18 @@ impl SourcemapBuilder {
     }
 
     pub fn add_source_mapping_for_name(&mut self, output: &[u8], span: Span, name: &str) {
-        // SAFETY: search original string by span.
-        let original_name =
-            unsafe { self.original_source.get_unchecked(span.start as usize..span.end as usize) };
+        debug_assert!(
+            (span.end as usize) <= self.original_source.len(),
+            "violated {}:{} <= {} for {name}",
+            span.start,
+            span.end,
+            self.original_source.len()
+        );
+        let original_name = self.original_source.get(span.start as usize..span.end as usize);
         // The token name should be original name.
         // If it hasn't change, name should be `None` to reduce `SourceMap` size.
-        let token_name = if original_name == name { None } else { Some(original_name.into()) };
+        let token_name =
+            if original_name == Some(name) { None } else { original_name.map(Into::into) };
         self.add_source_mapping(output, span.start, token_name);
     }