diff --git a/README.md b/README.md
index ec8bf89..4d2c158 100644
--- a/README.md
+++ b/README.md
@@ -206,7 +206,7 @@ module.exports = {
     // The file where the commit hashes will be stored
   , "path": "~/.git-stats"
 
-    // First day of the week
+    // [DEPRECATED] First day of the week https://github.com/IonicaBizau/git-stats/issues/121
   , first_day: "Sun"
 
     // This defaults to *one year ago*
diff --git a/lib/index.js b/lib/index.js
index 70cf452..44c4ca1 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -469,7 +469,7 @@ class GitStats {
                     theme: options.theme
                   , start: options.start
                   , end: options.end
-                  , firstDay: options.firstDay
+                  , firstDay: options.firstDay // [DEPRECATED] https://github.com/IonicaBizau/git-stats/issues/121
                   , cal: cal
                   , raw: options.raw
                 }
@@ -661,6 +661,7 @@ GitStats.DEFAULT_CONFIG = {
     // This defaults in library
   , path: undefined
 
+    // [DEPRECATED] https://github.com/IonicaBizau/git-stats/issues/121
     // This defaults in cli-gh-cal
   , first_day: undefined
 
diff --git a/package.json b/package.json
index 60ccc54..49073a5 100644
--- a/package.json
+++ b/package.json
@@ -192,7 +192,7 @@
             "    // The file where the commit hashes will be stored",
             "  , \"path\": \"~/.git-stats\"",
             "",
-            "    // First day of the week",
+            "    // [DEPRECATED] First day of the week https://github.com/IonicaBizau/git-stats/issues/121"
             "  , first_day: \"Sun\"",
             "",
             "    // This defaults to *one year ago*",
@@ -286,4 +286,4 @@
     "bloggify.json",
     "bloggify/"
   ]
-}
\ No newline at end of file
+}