diff --git a/src/index.ts b/src/index.ts
index 3f90cfc..0497335 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -27,9 +27,10 @@ const PLUGIN_NAME = 'vite:istanbul';
 const MODULE_PREFIX = '/@modules/';
 const NULL_STRING = '\0';
 
-function sanitizeSourceMap(sourceMap: ExistingRawSourceMap): ExistingRawSourceMap {
-  // delete sourcesContent since it is optional and if it contains process.env.NODE_ENV vite will try and replace it and break
-  delete sourceMap.sourcesContent;
+function sanitizeSourceMap(rawSourceMap: ExistingRawSourceMap): ExistingRawSourceMap {
+  // Delete sourcesContent since it is optional and if it contains process.env.NODE_ENV vite will break when trying to replace it
+  const { sourcesContent, ...sourceMap } = rawSourceMap;
+
   // JSON parse/stringify trick required for istanbul to accept the SourceMap
   return JSON.parse(JSON.stringify(sourceMap));
 }
diff --git a/src/types.d.ts b/src/types.d.ts
index 76566d8..e5c47fb 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -1,7 +1,8 @@
 declare module 'istanbul-lib-instrument' {
   import { ExistingRawSourceMap } from 'rollup';
+
   interface Instrumenter {
-    instrumentSync(code: string, filename: string, inputSourceMap?: ExistingRawSourceMap | undefined): string;
+    instrumentSync(code: string, filename: string, inputSourceMap?: ExistingRawSourceMap): string;
     lastSourceMap(): ExistingRawSourceMap;
   }
 
@@ -27,5 +28,6 @@ declare module 'test-exclude' {
 
     shouldInstrument(filePath:string):boolean
   }
+
   export = TestExclude
 }