diff --git a/.gdbinit b/.gdbinit
index 956a53471b..b67115b6a2 100644
--- a/.gdbinit
+++ b/.gdbinit
@@ -89,7 +89,11 @@ define rp
     echo undef\n
   else
   if (VALUE)($arg0) & RUBY_IMMEDIATE_MASK
-    echo immediate\n
+    if ((VALUE)($arg0) & RUBY_FLONUM_MASK) == RUBY_FLONUM_FLAG
+      printf "FLONUM: %g\n", (double)rb_float_value($arg0)
+    else
+      echo immediate\n
+    end
   else
   set $flags = ((struct RBasic*)($arg0))->flags
   if ($flags & RUBY_T_MASK) == RUBY_T_NONE
diff --git a/ChangeLog b/ChangeLog
index a305df6e83..17e5106737 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,9 @@
-Thu Sep  6 14:48:31 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Thu Sep  6 14:49:49 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* .gdbinit (rp): FLONUM support.
+
+	* include/ruby/ruby.h (ruby_special_consts): define FLONUM constants
+	  always, so that they are available from gdb.
 
 	* include/ruby/ruby.h (RB_FLOAT_TYPE_P): merge FLONUM and non-FLONUM
 	  versions.  inline TYPE() comparison and FLONUM_P() should be
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 61a5a50eeb..bab4a00bda 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -410,6 +410,8 @@ enum ruby_special_consts {
 
     RUBY_IMMEDIATE_MASK = 0x03,
     RUBY_FIXNUM_FLAG    = 0x01,
+    RUBY_FLONUM_MASK    = 0x00,	/* any values ANDed with FLONUM_MASK cannot be FLONUM_FLAG */
+    RUBY_FLONUM_FLAG    = 0x02,
     RUBY_SYMBOL_FLAG    = 0x0e,
     RUBY_SPECIAL_SHIFT  = 8
 #endif