diff --git a/src/util.js b/src/util.js
index 7564eee..be93e41 100644
--- a/src/util.js
+++ b/src/util.js
@@ -16,7 +16,7 @@ function fixWebpackFilePath(filePath) {
 function fixPathSeparators(filePath) {
   const isWin = process.platform.startsWith('win');
   // Workaround for https://github.com/mattlewis92/karma-coverage-istanbul-reporter/issues/9
-  if (isWin) {
+  if (isWin && filePath) {
     return filePath.replace(/\//g, '\\');
   }
   return filePath;
@@ -38,9 +38,8 @@ function fixWebpackSourcePaths(sourceMap, webpackConfig) {
 
   sourceRoot = fixPathSeparators(sourceRoot);
 
-  return Object.assign({}, sourceMap, {
+  const result = Object.assign({}, sourceMap, {
     file: fixPathSeparators(sourceMap.file),
-    sourceRoot,
     sources: (sourceMap.sources || []).map(source => {
       source = fixWebpackFilePath(source);
       if (sourceRoot && source.startsWith(sourceRoot)) {
@@ -49,6 +48,12 @@ function fixWebpackSourcePaths(sourceMap, webpackConfig) {
       return source;
     })
   });
+
+  if (sourceRoot) {
+    result.sourceRoot = sourceRoot;
+  }
+
+  return result;
 }
 
 function isAbsolute(file) {
diff --git a/test/util.spec.js b/test/util.spec.js
index 32af7bb..2c36b9a 100644
--- a/test/util.spec.js
+++ b/test/util.spec.js
@@ -78,6 +78,29 @@ describe('util', () => {
       expect(fixWebpackSourcePaths(input)).to.deep.equal(output);
     });
 
+    it('should handle undefined source roots', () => {
+      Object.defineProperty(process, 'platform', {
+        value: 'win32'
+      });
+      const input = {
+        file:
+          'C:/development/git/coverage-istanbul-reporter-path/client/modules/app/app.component.ts',
+        sources: [
+          'C:\\development\\git\\coverage-istanbul-reporter-path\\client\\modules\\app\\app.component.ts'
+        ] // eslint-disable-line unicorn/escape-case
+      };
+
+      const output = {
+        file:
+          'C:\\development\\git\\coverage-istanbul-reporter-path\\client\\modules\\app\\app.component.ts',
+        sources: [
+          'C:\\development\\git\\coverage-istanbul-reporter-path\\client\\modules\\app\\app.component.ts'
+        ]
+      };
+
+      expect(fixWebpackSourcePaths(input)).to.deep.equal(output);
+    });
+
     it('should not correct path separators on non windows systems', () => {
       const input = {
         file: '/foo/bar',