diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 77c419b..86bde47 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,8 +1,10 @@
 # Coding standards
 
-* 4 spaces are used for tabulation.
+* 4 spaces are used for tabulation. No tabs are allowed.
 * Unix line endings are used.
 * Curlies are always explicitly written.
+* No trailing whitespaces at the end of lines.
+* Insert closing newline at the end of files.
 
 ## If