diff --git a/ChangeLog b/ChangeLog
index 1e996b7d2b..b10df610e6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2018-06-25  Rafal Luzynski  <digitalfreak@lingonborough.com>
+
+	[BZ #23140]
+	* localedata/locales/csb_PL (mon): Rename to...
+	(alt_mon): This.
+	(abmon): Rename to...
+	(ab_alt_mon): This.
+	(mon): Add with proper genitive forms, copy from Wikipedia.
+	(abmon): Likewise.
+
 2018-06-25  Rafal Luzynski  <digitalfreak@lingonborough.com>
 
 	[BZ #19485]
diff --git a/NEWS b/NEWS
index d51fa09544..db7c1291fd 100644
--- a/NEWS
+++ b/NEWS
@@ -25,9 +25,9 @@ Major new features:
     fMxdivfNx functions.
 
 * Nominative and genitive month names are now supported for the following
-  languages: Catalan, Czech, Scottish Gaelic, Upper Sorbian, and Walloon.
-  The Catalan and Greek languages now support abbreviated alternative
-  month names.
+  languages: Catalan, Czech, Kashubian, Scottish Gaelic, Upper Sorbian,
+  and Walloon.  The following languages now support abbreviated alternative
+  month names: Catalan, Greek, and Kashubian.
 
 * Building and running on GNU/Hurd systems now works without out-of-tree
   patches.
diff --git a/localedata/locales/csb_PL b/localedata/locales/csb_PL
index fa82966b16..c8572f8fc5 100644
--- a/localedata/locales/csb_PL
+++ b/localedata/locales/csb_PL
@@ -147,13 +147,19 @@ day    "niedzela";/
         "czwi<U00F4>rtk";/
         "pi<U0105>tk";/
         "sob<U00F2>ta"
-abmon  "st<U00EB>"; "gro";/
+ab_alt_mon "st<U00EB>"; "gro";/
         "str"; "<U0142><U017C><U00EB>";/
         "m<U00F4>j"; "cze";/
         "l<U00EB>p"; "z<U00E9>l";/
         "s<U00E9>w"; "ruj";/
         "l<U00EB>s"; "g<U00F2>d"
-mon    "st<U00EB>cznik";/
+abmon   "st<U00EB>"; "gro";/
+        "str"; "<U0142><U017C><U00EB>";/
+        "maj"; "cze";/
+        "l<U00EB>p"; "z<U00E9>l";/
+        "s<U00E9>w"; "ruj";/
+        "l<U00EB>s"; "g<U00F2>d"
+alt_mon "st<U00EB>cznik";/
         "gromicznik";/
         "str<U00EB>miannik";/
         "<U0142><U017C><U00EB>kwiat";/
@@ -165,6 +171,18 @@ mon    "st<U00EB>cznik";/
         "rujan";/
         "l<U00EB>stopadnik";/
         "g<U00F2>dnik"
+mon     "st<U00EB>cznika";/
+        "gromicznika";/
+        "str<U00EB>miannika";/
+        "<U0142><U017C><U00EB>kwiata";/
+        "maja";/
+        "czerwi<U0144>ca";/
+        "l<U00EB>pi<U0144>ca";/
+        "z<U00E9>lnika";/
+        "s<U00E9>wnika";/
+        "rujana";/
+        "l<U00EB>stopadnika";/
+        "g<U00F2>dnika"
 d_t_fmt "%a %d %b %Y %T %Z"
 d_fmt   "%Y-%m-%d"
 t_fmt   "%T"