--- a/build/macosx/local-mozconfig.common
+++ b/build/macosx/local-mozconfig.common
@@ -27,16 +27,21 @@ elif [ -d "$topsrcdir/../clang" ]; then
     ldflags="-B$topsrcdir/../cctools/bin"
 fi
 
 # Ensure the updated linker doesn't generate things our older build tools
 # don't understand.
 ldflags="$ldflags -Wl,-no_data_in_code_info"
 export LDFLAGS="$ldflags"
 
+# Until bug 1342503 is fixed, we can't build some of the webrender dependencies
+# on buildbot OS X builders, because rustc will use some random system toolchain
+# instead of the one we package with tooltool.
+ac_add_options --disable-webrender
+
 # If not set use the system default clang
 if [ -z "$CC" ]; then
     export CC=clang
 fi
 
 # If not set use the system default clang++
 if [ -z "$CXX" ]; then
     export CXX=clang++