diff --git a/ChangeLog b/ChangeLog
index f6a9c0715e..6e9d2ef6ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat May 24 00:25:34 2014  Ayumu AIZAWA  <ayumu.aizawa@gmail.com>
+
+	* NEWS: add information of incompatibility about Prime.prime?
+	* lib/prime.rb: fix docs.
+
 Fri May 23 21:36:28 2014  Josh Goebel  <dreamer3@gmail.com>
 
 	* net/protocol.rb (using_each_crlf_line): fix SMTP dot-stuffing
diff --git a/NEWS b/NEWS
index 8bc0625f8a..d6a97dabda 100644
--- a/NEWS
+++ b/NEWS
@@ -111,6 +111,11 @@ with all sufficient information, see the ChangeLog file.
   * Removed because it conflicts to minitest 5, and it was just an wrapper
     of minitest 4. [Feature #9711]
 
+* Prime
+  * incompatible changes:
+    * Prime.prime? now returns false for negative numbers. This method
+      should not be used to know the number is composite or not. [Bug #7395]
+
 === Built-in global variables compatibility issues
 
 === C API updates
diff --git a/lib/prime.rb b/lib/prime.rb
index 6d3936e317..4b14a221f7 100644
--- a/lib/prime.rb
+++ b/lib/prime.rb
@@ -29,7 +29,7 @@ class Integer
     Prime.prime_division(self, generator)
   end
 
-  # Returns true if +self+ is a prime number, false for a composite.
+  # Returns true if +self+ is a prime number, else returns false.
   def prime?
     Prime.prime?(self)
   end
@@ -150,7 +150,7 @@ class Prime
   end
 
 
-  # Returns true if +value+ is prime, false for a composite.
+  # Returns true if +value+ is prime number, else returns false.
   #
   # == Parameters
   #