diff --git a/scripts/prepare.js b/scripts/prepare.js
index 2e69591f0..6dbf4031c 100644
--- a/scripts/prepare.js
+++ b/scripts/prepare.js
@@ -18,8 +18,8 @@ const pkgFiles = readJSON('package.json').files;
 // Get only negated patterns.
 const ignorePatterns = pkgFiles
   .filter(pat => pat.startsWith('!'))
-// Remove the negation part. Makes micromatch usage more intuitive.
-  .map(pat => pat.slice(1));
+// Remove the negation part and initial slash. Makes micromatch usage more intuitive.
+  .map(pat => pat.slice(1).replace(/^\//, ''));
 
 const ignorePatternsSubtrees = ignorePatterns
 // Add **/* to ignore all files contained in the directories.