diff --git a/bignum.c b/bignum.c
index f806558b97..96488b4b1c 100644
--- a/bignum.c
+++ b/bignum.c
@@ -7115,6 +7115,7 @@ Init_Bignum(void)
 #ifndef RUBY_INTEGER_UNIFICATION
     rb_cBignum = rb_cInteger;
 #endif
+    /* An obsolete class, use Integer */
     rb_define_const(rb_cObject, "Bignum", rb_cInteger);
     rb_deprecate_constant(rb_cObject, "Bignum");
 
diff --git a/numeric.c b/numeric.c
index c5ff98b7d7..01856c7f20 100644
--- a/numeric.c
+++ b/numeric.c
@@ -5460,6 +5460,7 @@ Init_Numeric(void)
 #ifndef RUBY_INTEGER_UNIFICATION
     rb_cFixnum = rb_cInteger;
 #endif
+    /* An obsolete class, use Integer */
     rb_define_const(rb_cObject, "Fixnum", rb_cInteger);
     rb_deprecate_constant(rb_cObject, "Fixnum");
 
diff --git a/process.c b/process.c
index a09c3e18e6..70a2eef67f 100644
--- a/process.c
+++ b/process.c
@@ -7975,7 +7975,8 @@ InitVM_process(void)
 
 #if defined(HAVE_TIMES) || defined(_WIN32)
     rb_cProcessTms = rb_struct_define_under(rb_mProcess, "Tms", "utime", "stime", "cutime", "cstime", NULL);
-    rb_define_const(rb_cStruct, "Tms", rb_cProcessTms); /* for the backward compatibility */
+    /* An obsolete name of Process::Tms for the backward compatibility */
+    rb_define_const(rb_cStruct, "Tms", rb_cProcessTms);
     rb_deprecate_constant(rb_cStruct, "Tms");
 #endif