diff -ruN b/acinclude.m4 a/acinclude.m4
--- b/acinclude.m4	2006-03-12 01:03:51.000000000 +0300
+++ a/acinclude.m4	2006-06-28 01:20:00.000000000 +0400
@@ -458,12 +458,14 @@
         yes)
 			AC_DEFINE([OGRE_DOUBLE_PRECISION], [1], [Build with double precision])
 			AC_MSG_RESULT(yes)
+			OGRE_DOUBLE_PRECISION_FLAGS="-DOGRE_DOUBLE_PRECISION"
         ;;
         *)
 			AC_DEFINE([OGRE_DOUBLE_PRECISION], [0], [Build with double precision])
             AC_MSG_RESULT(no)
         ;;
     esac
+    AC_SUBST(OGRE_DOUBLE_PRECISION_FLAGS)
 ])
 
 AC_DEFUN([OGRE_CHECK_THREADING],
diff -ruN b/OGRE.pc.in a/OGRE.pc.in
--- b/OGRE.pc.in	2006-02-03 07:04:39.000000000 +0300
+++ a/OGRE.pc.in	2006-06-28 01:19:19.000000000 +0400
@@ -8,4 +8,4 @@
 Description: Object-Oriented Graphics Rendering Engine
 Version: @VERSION@
 Libs: -L${libdir} -lOgreMain
-Cflags: -I${includedir} -I${includedir}/@PACKAGE@
+Cflags: -I${includedir} -I${includedir}/@PACKAGE@ @OGRE_DOUBLE_PRECISION_FLAGS@