diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1b980764..5a1785c6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -19,6 +19,39 @@ set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake/modules" )
 
 include (SetPaths.cmake)
 
+###############################################################################
+# Set defaults for Universal Binaries. We want 32-bit Intel/PPC on 10.4 
+# and 32/64-bit Intel/PPC on >= 10.5. Anything <= 10.3 doesn't support.
+IF(APPLE)
+    # These are just defaults/recommendations, but how we want to build
+    # out of the box. But the user needs to be able to change these options.
+    # So we must only set the values the first time CMake is run, or we 
+    # will overwrite any changes the user sets.
+    # FORCE is used because the options are not reflected in the UI otherwise.
+    IF(NOT "${OPENTHREADS_CONFIG_HAS_BEEN_RUN_BEFORE}")
+        # This is really fragile, but CMake doesn't provide the OS system 
+        # version information we need. (Darwin versions can be changed 
+        # independently of OS X versions.)
+        # It does look like CMake handles the CMAKE_OSX_SYSROOT automatically.
+        IF(EXISTS /Developer/SDKs/10.5.sdk)
+#Qt does not support ppc64 and x86_64
+#            SET(CMAKE_OSX_ARCHITECTURES "ppc;i386;ppc64;x86_64" CACHE STRING "Build architectures for OSX" FORCE)
+            SET(CMAKE_OSX_ARCHITECTURES "ppc;i386" CACHE STRING "Build architectures for OSX" FORCE)
+            SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility-inlines-hidden" CACHE STRING "Flags used by the compiler during all build types." FORCE)
+        ELSE(EXISTS /Developer/SDKs/10.5.sdk)
+            IF(EXISTS /Developer/SDKs/MacOSX10.4u.sdk)
+#Qt does not support ppc64 and x86_64
+#                SET(CMAKE_OSX_ARCHITECTURES "ppc;i386;ppc64;x86_64" CACHE STRING "Build architectures for OSX" FORCE)
+                SET(CMAKE_OSX_ARCHITECTURES "ppc;i386" CACHE STRING "Build architectures for OSX" FORCE)
+                SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility-inlines-hidden" CACHE STRING "Flags used by the compiler during all build types." FORCE)
+            ELSE(EXISTS /Developer/SDKs/MacOSX10.4u.sdk)
+                # No Universal Binary support
+            ENDIF(EXISTS /Developer/SDKs/MacOSX10.4u.sdk)
+        ENDIF(EXISTS /Developer/SDKs/10.5.sdk)
+    ENDIF(NOT "${OPENTHREADS_CONFIG_HAS_BEEN_RUN_BEFORE}")
+ENDIF(APPLE)
+
+
 add_subdirectory(backend)
 add_subdirectory(frontend)