diff --git a/collects/meta/build/build b/collects/meta/build/build
index 39400647f1..5ffb82c42e 100755
--- a/collects/meta/build/build
+++ b/collects/meta/build/build
@@ -85,12 +85,12 @@ defbuild "pitcairn2" "x86_64-win32" "test_gui=yes" \
          "workdir=C:/build" # same here (see also commit log!)
 # The LDFLAGS is a workaround for a bug in Fink, see
 # http://wiki.finkproject.org/index.php/Fink:Packaging:Preparing_for_10.5#OpenGL_Bug
-defbuild "kauai"       "ppc-darwin" "configure_args=--enable-xonx" \
+defbuild "kauai"       "ppc-darwin" "configure_args='--enable-xonx --disable-mac64'" \
   "LDFLAGS=-dylib_file /System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL.dylib:/System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL.dylib"
 defbuild "weatherwax"  "ppc-osx-mac" \
          "configure_args=--enable-sdk=/Developer/SDKs/MacOSX10.4u.sdk"
 defbuild "macintel"    "i386-osx-mac" \
-         "configure_args=--enable-sdk=/Developer/SDKs/MacOSX10.4u.sdk"
+         "configure_args='--enable-sdk=/Developer/SDKs/MacOSX10.4u.sdk --disable-mac64'"
 # defbuild "galaga"      "i386-linux-ubuntu-hardy"
 defbuild "champlain"   "i386-linux-f12"
 defbuild "ccs-linux"   "i386-linux-ubuntu-karmic" "moveto=/proj/racket"
@@ -104,7 +104,7 @@ defbuild "ccs-linux"   "i386-linux-ubuntu-karmic" "moveto=/proj/racket"
 defbuild "blisses1" "x86_64-linux-debian-lenny"
 defbuild "blisses2" "x86_64-linux-debian-squeeze"
 # And this is from Stephen De Gabrielle <stephen.degabrielle at acm dot org>
-defbuild "osx64" "x86_64-osx-mac" "configure_args=--enable-mac64"
+defbuild "osx64" "x86_64-osx-mac"
 # Start the main build last
 defbuild "$workmachine" "x86_64-linux-f14" "copytobak=$maindir" "test_gui=yes"
 msets "/"
diff --git a/src/README b/src/README
index 7dda3e5632..d6bf7c5d86 100644
--- a/src/README
+++ b/src/README
@@ -68,9 +68,8 @@ the Unix instructions below, but note the following:
    directory structure on top of an existing Unix-style directory
    structure.)
 
- * Under Mac OS X 10.6 and later, `configure' by default selects
-   32-bit mode for building Racket.  To build Racket in 64-bit mode,
-   use `--enable-mac64'.
+ * Under Mac OS X 10.6 and later, to build Racket in 32-bit mode,
+   use `--disable-mac64'.
 
 ========================================================================
  Compiling for supported Unix variants (including Linux) or Cygwin
diff --git a/src/configure b/src/configure
index 45d1c57a96..a075ff50c5 100755
--- a/src/configure
+++ b/src/configure
@@ -1349,7 +1349,7 @@ Optional Features:
   --enable-libfw          install Mac OS X frameworks to /Library/Frameworks
   --enable-userfw         install Mac OS X frameworks to ~/Library/Frameworks
   --enable-macprefix      allow --prefix with a Mac OS X install
-  --enable-mac64          do not force 32-bit build
+  --enable-mac64          allow 64-bit Mac OS X build (enabled by default)
   --enable-cgcdefault     use CGC (Boehm or Senora) as default build
   --enable-sgc            use Senora GC instead of the Boehm GC
   --enable-sgcdebug       use Senora GC for debugging
@@ -2084,6 +2084,8 @@ fi
 # Check whether --enable-mac64 was given.
 if test "${enable_mac64+set}" = set; then
   enableval=$enable_mac64;
+else
+  enable_mac64=yes
 fi
 
 
@@ -2345,7 +2347,7 @@ show_explicitly_enabled "${enable_gcov}" "gcov"
 
 show_explicitly_enabled "${enable_noopt}" "No-optimization"
 
-show_explicitly_enabled "${enable_mac64}" "64-bit Mac OS X"
+show_explicitly_disabled "${enable_mac64}" "64-bit Mac OS X"
 
 show_explicitly_enabled "${enable_libfw}" "Frameworks-to-system"
 show_explicitly_enabled "${enable_userfw}" "Frameworks-to-user"
diff --git a/src/racket/configure.ac b/src/racket/configure.ac
index b7d5deff52..a3e1b572a3 100644
--- a/src/racket/configure.ac
+++ b/src/racket/configure.ac
@@ -52,7 +52,7 @@ AC_ARG_ENABLE(xonx,    [  --enable-xonx           use Unix style (e.g., use Gtk)
 AC_ARG_ENABLE(libfw,   [  --enable-libfw          install Mac OS X frameworks to /Library/Frameworks])
 AC_ARG_ENABLE(libfw,   [  --enable-userfw         install Mac OS X frameworks to ~/Library/Frameworks])
 AC_ARG_ENABLE(macprefix, [  --enable-macprefix      allow --prefix with a Mac OS X install])
-AC_ARG_ENABLE(mac64,   [  --enable-mac64          do not force 32-bit build])
+AC_ARG_ENABLE(mac64,   [  --enable-mac64          allow 64-bit Mac OS X build (enabled by default)], , enable_mac64=yes)
 
 AC_ARG_ENABLE(cgcdefault, [  --enable-cgcdefault     use CGC (Boehm or Senora) as default build])
 AC_ARG_ENABLE(sgc,     [  --enable-sgc            use Senora GC instead of the Boehm GC])
@@ -272,7 +272,7 @@ show_explicitly_enabled "${enable_gcov}" "gcov"
 
 show_explicitly_enabled "${enable_noopt}" "No-optimization"
 
-show_explicitly_enabled "${enable_mac64}" "64-bit Mac OS X"
+show_explicitly_disabled "${enable_mac64}" "64-bit Mac OS X"
 
 show_explicitly_enabled "${enable_libfw}" "Frameworks-to-system"
 show_explicitly_enabled "${enable_userfw}" "Frameworks-to-user"