diff --git a/mac_build/buildWxMac.sh b/mac_build/buildWxMac.sh
index d0a9e584c2..cca59fa79f 100644
--- a/mac_build/buildWxMac.sh
+++ b/mac_build/buildWxMac.sh
@@ -2,7 +2,7 @@
 
 # This file is part of BOINC.
 # http://boinc.berkeley.edu
-# Copyright (C) 2017 University of California
+# Copyright (C) 2018 University of California
 #
 # BOINC is free software; you can redistribute it and/or modify it
 # under the terms of the GNU Lesser General Public License
@@ -36,6 +36,7 @@
 # Update for wxCocoa 3.1.0 10/25/17
 # Build only 64-bit library 1/25/18
 # Fix wxWidgets 3.1.0 bug when wxStaticBox has no label 3/20/18
+# Fix wxWidgets 3.1.0 to not use backingScaleFactor API on OS 10.6 6/8/18
 #
 ## This script requires OS 10.6 or later
 ##
@@ -133,7 +134,7 @@ else
     echo "build/osx/setup/cocoa/include/wx/setup.h already patched"
 fi
 
-# Patch src/osx/window_osx.cpp window_osx_patched.cpp > window_osx_cpp_diff
+# Patch src/osx/window_osx.cpp
 if [ ! -f src/osx/window_osx.cpp.orig ]; then
     cat >> /tmp/window_osx_cpp_diff << ENDOFFILE
 --- window_osx.cpp    2016-02-28 13:33:37.000000000 -0800
@@ -155,6 +156,54 @@ else
     echo "src/osx/window_osx.cpp already patched"
 fi
 
+# Patch src/osx/carbon/utilscocoa.mm
+if [ ! -f src/osx/carbon/utilscocoa.mm.orig ]; then
+    cat >> /tmp/utilscocoa_mm_diff << ENDOFFILE
+--- utilscocoa.mm    2016-02-28 13:33:37.000000000 -0800
++++ utilscocoa-patched.mm    2018-06-03 01:31:43.000000000 -0700
+@@ -476,7 +476,10 @@
+ 
+ double wxOSXGetMainScreenContentScaleFactor()
+ {
+-    return [[NSScreen mainScreen] backingScaleFactor];
++    if ([[NSScreen mainScreen] respondsToSelector:@selector(backingScaleFactor)])
++        return [[NSScreen mainScreen] backingScaleFactor];
++    else
++        return 1.0;
+ }
+ 
+ CGImageRef wxOSXCreateCGImageFromNSImage( WX_NSImage nsimage, double *scaleptr )
+ENDOFFILE
+    patch -bfi /tmp/utilscocoa_mm_diff src/osx/carbon/utilscocoa.mm
+    rm -f /tmp/utilscocoa_mm_diff
+else
+    echo "src/osx/carbon/utilscocoa.mm already patched"
+fi
+
+# Patch src/osx/cocoa/window.mm
+if [ ! -f src/osx/cocoa/window.mm.orig ]; then
+    cat >> /tmp/window_mm_diff << ENDOFFILE
+--- window.mm    2016-02-28 13:33:37.000000000 -0800
++++ window-patched.mm    2018-06-08 01:28:01.000000000 -0700
+@@ -1869,7 +1869,10 @@
+ double wxWidgetCocoaImpl::GetContentScaleFactor() const
+ {
+     NSWindow* tlw = [m_osxView window];
+-    return [tlw backingScaleFactor];
++    if ([tlw respondsToSelector:@selector(backingScaleFactor)])
++        return [tlw backingScaleFactor];
++    else
++        return 1.0;
+ }
+ 
+ // ----------------------------------------------------------------------------
+ENDOFFILE
+    patch -bfi /tmp/window_mm_diff src/osx/cocoa/window.mm
+    rm -f /tmp/window_mm_diff
+else
+    echo "src/osx/cocoa/window.mm already patched"
+fi
+
 
 echo ""