diff --git a/DepotDownloader/CDRManager.cs b/DepotDownloader/CDRManager.cs
index 8df5e5ab..8630cf58 100644
--- a/DepotDownloader/CDRManager.cs
+++ b/DepotDownloader/CDRManager.cs
@@ -230,7 +230,7 @@ namespace DepotDownloader
 
             if ( platform == PlatformID.Win32NT )
                 platformStr = "windows";
-            else if ( platform == PlatformID.MacOSX )
+            else if ( Util.IsMacOSX() )
                 platformStr = "macos";
             
             foreach ( var blobField in appInfoBlob.FileSystems )
@@ -266,7 +266,7 @@ namespace DepotDownloader
 
                 if (platform == PlatformID.Win32NT)
                     platformSuffix = "-win32";
-                else if (platform == PlatformID.Unix)
+                else if (platform == PlatformID.Unix && !Util.IsMacOSX())
                     platformSuffix = "-linux";
 
                 foreach (var blobField in serverAppInfoBlob.FileSystems)
@@ -301,7 +301,7 @@ namespace DepotDownloader
                 }
                 else if ( platform == PlatformID.Win32NT )
                     appIDs.Add( 5 );
-                else if ( platform == PlatformID.Unix)
+                else if ( platform == PlatformID.Unix && !Util.IsMacOSX() )
                     appIDs.Add( 4 );
 
                 // Half-Life Base Content
diff --git a/DepotDownloader/Util.cs b/DepotDownloader/Util.cs
index 55732c55..9a787c7c 100644
--- a/DepotDownloader/Util.cs
+++ b/DepotDownloader/Util.cs
@@ -11,6 +11,49 @@ namespace DepotDownloader
 {
     static class Util
     {
+        [DllImport( "libc" )]
+        static extern int uname( IntPtr buf );
+
+        static int _isMacOSX = -1;
+
+        // Environment.OSVersion.Platform returns PlatformID.Unix under Mono on OS X
+        // Code adapted from Mono: mcs/class/Managed.Windows.Forms/System.Windows.Forms/XplatUI.cs
+        public static bool IsMacOSX()
+        {
+            if ( _isMacOSX != -1 )
+                return _isMacOSX == 1;
+
+            IntPtr buf = IntPtr.Zero;
+
+            try
+            {
+                // The size of the utsname struct varies from system to system, but this _seems_ more than enough
+                buf = Marshal.AllocHGlobal( 4096 );
+
+                if ( uname( buf ) == 0 )
+                {
+                    string sys = Marshal.PtrToStringAnsi( buf );
+                    if ( sys == "Darwin" )
+                    {
+                        _isMacOSX = 1;
+                        return true;
+                    }
+                }
+            }
+            catch
+            {
+                // Do nothing?
+            }
+            finally
+            {
+                if ( buf != IntPtr.Zero )
+                    Marshal.FreeHGlobal( buf );
+            }
+
+            _isMacOSX = 0;
+            return false;
+        }
+
         public static string ReadPassword()
         {
             ConsoleKeyInfo keyInfo;