diff --git a/checkin_notes b/checkin_notes
index d292cb69b3..d71cb687c9 100644
--- a/checkin_notes
+++ b/checkin_notes
@@ -750,3 +750,11 @@ David  14 Feb 2011
     configure.ac
     client/
         hostinfo_unix.cpp
+
+Charlie 15 Feb 2011
+    Mac: Make backtrace compile properly with OS 10.5 and OS 10.6 SDKs.
+    
+    lib/
+        QBacktrace.c
+        QCrashReport.c
+ 
\ No newline at end of file
diff --git a/lib/mac/QBacktrace.c b/lib/mac/QBacktrace.c
index fe9b8b50bd..ce5e6f5140 100644
--- a/lib/mac/QBacktrace.c
+++ b/lib/mac/QBacktrace.c
@@ -109,6 +109,12 @@ First checked in.
 
 /////////////////////////////////////////////////////////////////
 
+// Compatibility with OS 10.5 SDK and later
+#if __DARWIN_UNIX03
+#undef __DARWIN_UNIX03
+#endif
+#define __DARWIN_UNIX03 0
+
 // Our Prototypes
 
 #include "QBacktrace.h"
@@ -140,6 +146,7 @@ First checked in.
 // By default, the system only gives us the one that's appropriate 
 // for our machine.  So we include both here.
 
+
 #include <mach/ppc/thread_status.h>
 #include <mach/i386/thread_status.h>
 
diff --git a/lib/mac/QCrashReport.c b/lib/mac/QCrashReport.c
index ecf327f5bd..cb1b403d9b 100644
--- a/lib/mac/QCrashReport.c
+++ b/lib/mac/QCrashReport.c
@@ -106,6 +106,12 @@ First checked in.
 
 /////////////////////////////////////////////////////////////////
 
+// Compatibility with OS 10.5 SDK and later
+#if __DARWIN_UNIX03
+#undef __DARWIN_UNIX03
+#endif
+#define __DARWIN_UNIX03 0
+
 #include "config.h"
 #include "QCrashReport.h"
 #include "mac_backtrace.h"