diff --git a/lib/random/formatter.rb b/lib/random/formatter.rb
index c48886f9e0..0e80bd0f70 100644
--- a/lib/random/formatter.rb
+++ b/lib/random/formatter.rb
@@ -3,6 +3,8 @@
 
 # == Random number formatter.
 #
+# Formats generated random numbers in many manors.
+#
 # === Examples
 #
 # Generate random hexadecimal strings:
diff --git a/random.c b/random.c
index 580c1f26eb..32c470bdad 100644
--- a/random.c
+++ b/random.c
@@ -1807,7 +1807,14 @@ InitVM_Random(void)
     rb_define_private_method(CLASS_OF(rb_cRandom), "left", random_s_left, 0);
 
     {
-	/* Format raw random number as Random does */
+	/*
+         * Generate a random number in the given range as Random does
+         *
+         *   prng.random_number       #=> 0.5816771641321361
+         *   prng.random_number(1000) #=> 485
+         *   prng.rand                #=> 0.5816771641321361
+         *   prng.rand(1000)          #=> 485
+         */
 	VALUE m = rb_define_module_under(rb_cRandom, "Formatter");
 	rb_include_module(base, m);
 	rb_extend_object(base, m);