diff --git a/crates/swc_common/src/source_map.rs b/crates/swc_common/src/source_map.rs
index 249d7b8a73d..8c837fd3468 100644
--- a/crates/swc_common/src/source_map.rs
+++ b/crates/swc_common/src/source_map.rs
@@ -1145,11 +1145,10 @@ impl SourceMap {
 
         if let Some(orig) = orig {
             for src in orig.sources() {
-                let idx = builder.add_source(src);
-                src_id = idx as u32 + 1;
-            }
-            for (idx, contents) in orig.source_contents().enumerate() {
-                builder.set_source_contents(idx as _, contents);
+                let id = builder.add_source(src);
+                src_id = id as u32 + 1;
+
+                builder.set_source_contents(id, orig.get_source_contents(id));
             }
         }