diff --git a/checkin_notes b/checkin_notes
index 788b11af5c..df033cfb05 100644
--- a/checkin_notes
+++ b/checkin_notes
@@ -7519,3 +7519,12 @@ Rom    19 Oct 2010
     clientgui/
         AdvancedFrame.cpp
         NoticeListCtrl.cpp
+
+Charlie 16 Oct 2010
+    - lib: Mac backtrace code (including the backtrace() API) doesn't work 
+        on PowerPC Macs running under OS 10.5.x, so display explanatory text 
+        when attempting a backtrace on those machines.
+    
+    lib/
+        mac/
+            mac_backtrace.cpp
diff --git a/lib/mac/mac_backtrace.cpp b/lib/mac/mac_backtrace.cpp
index 5cd22665ba..ab2a3f62b6 100644
--- a/lib/mac/mac_backtrace.cpp
+++ b/lib/mac/mac_backtrace.cpp
@@ -47,6 +47,10 @@
 // The old way still seems to work better under OS 10.6.4
 #define USE_NEW_ROUTINES false  
 
+#ifdef __ppc__
+#include <Carbon/Carbon.h>
+#endif
+
 #include <mach-o/dyld.h>
 #include <mach-o/loader.h>
 #include <mach-o/nlist.h>
@@ -154,7 +158,16 @@ void PrintBacktrace(void) {
     fputs(asctime(localtime(&t)), stderr);
     fputc('\n', stderr);
     
-   err = QCRCreateFromSelf(&crRef);
+#ifdef __ppc__
+    long OSVersion = 0;
+    OSStatus gestaltErr = Gestalt(gestaltSystemVersion, &OSVersion);
+    if ((gestaltErr == noErr) && ((OSVersion & 0xfff0) == 0x1050)) {
+        fputs("BOINC backtrace is not supported for PowerPC under OS 10.5.x\n", stderr);
+        fputs("To get a backtrace run under OS 10.4.x or run on an Intel Mac\n\n", stderr);
+    }
+#endif
+
+    err = QCRCreateFromSelf(&crRef);
 
 #if USE_NEW_ROUTINES
     // Use new backtrace functions if available (only in OS 10.5 and later)