diff --git a/lib/core/file.js b/lib/core/file.js
index bc97ddaa..c81d3281 100644
--- a/lib/core/file.js
+++ b/lib/core/file.js
@@ -24,10 +24,11 @@ class File {
       // Only supported in Solidity
       return callback(null, content);
     }
-    const regex = /import ["|']([-a-zA-Z0-9@:%_+.~#?&\/=]+)["|'];/g;
+    const regex = /import ["']([-a-zA-Z0-9@:%_+.~#?&\/=]+)["'];/g;
     let matches;
     const filesToDownload = [];
     const pathWithoutFile = path.dirname(self.path);
+    let newContent = content;
     while ((matches = regex.exec(content))) {
       const httpFileObj = utils.getExternalContractUrl(matches[1]);
       const fileObj = {
@@ -36,7 +37,7 @@ class File {
       };
       if (httpFileObj) {
         // Replace http import by filePath import in content
-        content = content.replace(matches[1], httpFileObj.filePath);
+        newContent = newContent.replace(matches[1], httpFileObj.filePath);
 
         fileObj.fileRelativePath = httpFileObj.filePath;
         fileObj.url = httpFileObj.url;
@@ -49,7 +50,7 @@ class File {
 
     if (self.downloadedImports) {
       // We already parsed this file
-      return callback(null, content);
+      return callback(null, newContent);
     }
     self.downloadedImports = true;
     async.each(filesToDownload, ((fileObj, eachCb) => {
@@ -57,7 +58,7 @@ class File {
         eachCb();
       });
     }), (err) => {
-      callback(err, content);
+      callback(err, newContent);
     });
   }