diff --git a/.cross_rubies b/.cross_rubies
index eecbd327e0..f9828f42a8 100644
--- a/.cross_rubies
+++ b/.cross_rubies
@@ -2,19 +2,19 @@
 2.7.0:x86_64-w64-mingw32
 2.7.0:i686-linux-gnu
 2.7.0:x86_64-linux-gnu
-2.7.0:x86_64-darwin19
+2.7.0:x86_64-darwin
 2.6.0:i686-w64-mingw32
 2.6.0:x86_64-w64-mingw32
 2.6.0:i686-linux-gnu
 2.6.0:x86_64-linux-gnu
-2.6.0:x86_64-darwin19
+2.6.0:x86_64-darwin
 2.5.0:i686-w64-mingw32
 2.5.0:x86_64-w64-mingw32
 2.5.0:i686-linux-gnu
 2.5.0:x86_64-linux-gnu
-2.5.0:x86_64-darwin19
+2.5.0:x86_64-darwin
 2.4.0:i686-w64-mingw32
 2.4.0:x86_64-w64-mingw32
 2.4.0:i686-linux-gnu
 2.4.0:x86_64-linux-gnu
-2.4.0:x86_64-darwin19
+2.4.0:x86_64-darwin
diff --git a/scripts/setup-osx-native-builders b/scripts/setup-osx-native-builders
index bc276fe061..9dc8e3c822 100755
--- a/scripts/setup-osx-native-builders
+++ b/scripts/setup-osx-native-builders
@@ -4,6 +4,9 @@
 # - https://github.com/rake-compiler/rake-compiler/blob/master/tasks/bin/cross-ruby.rake
 # - https://github.com/apolcyn/grpc/blob/master/tools/distrib/build_ruby_environment_macos.sh
 
+# see test/test_gem_platform.rb for context
+gem_platform_name="x86_64-darwin"
+
 # chosen so chruby will see it, should you be a user of chruby
 RUBIES_DIR=${HOME}/.rubies
 
@@ -18,11 +21,12 @@ set -o pipefail
 
 CROSS_FILE=".cross_rubies"
 RUBIES=$(cat $CROSS_FILE | fgrep darwin | cut -d. -f1,2 | sort -u)
+
 RAKE_COMPILER_CONFIG_DIR=${HOME}/.rake-compiler
 RAKE_COMPILER_CONFIG=${RAKE_COMPILER_CONFIG_DIR}/config.yml
+TMP_CONFIG=$(mktemp /tmp/rake-compiler-config.XXXXXXXX)
 
-mkdir -p $RAKE_COMPILER_CONFIG_DIR
-echo "---" > $RAKE_COMPILER_CONFIG
+echo "---" > $TMP_CONFIG
 
 for ruby in $RUBIES ; do
   ruby_fullname="native-builder-${ruby}"
@@ -42,9 +46,9 @@ for ruby in $RUBIES ; do
     echo "ruby $ruby_fullname is installed"
   fi
 
-  platform=$(basename $(dirname $rbconfig))
-
-  echo "rbconfig-${platform}-${ruby_minor}: \"${rbconfig}\"" >> $RAKE_COMPILER_CONFIG
+  echo "rbconfig-${gem_platform_name}-${ruby_minor}: \"${rbconfig}\"" >> $TMP_CONFIG
 done
 
+mkdir -p $RAKE_COMPILER_CONFIG_DIR
+cp $TMP_CONFIG $RAKE_COMPILER_CONFIG
 cat $RAKE_COMPILER_CONFIG
diff --git a/tasks/cross-ruby.rb b/tasks/cross-ruby.rb
index 27a1599536..70ab06e9a0 100644
--- a/tasks/cross-ruby.rb
+++ b/tasks/cross-ruby.rb
@@ -43,8 +43,8 @@ def platform
         "x86_64-linux"
       when /\Ai[3-6]86.*linux/
         "x86-linux"
-      when /\Ax86_64-darwin19/
-        "x86_64-darwin19"
+      when /\Ax86_64-darwin/
+        "x86_64-darwin"
       else
         raise "CrossRuby.platform: unsupported host: #{host}"
       end
@@ -60,8 +60,8 @@ def tool(name)
         "x86_64-linux-gnu-"
       when "x86-linux"
         "i686-linux-gnu-"
-      when /darwin/
-        ""
+      # when /darwin/
+      #   ""
       else
         raise "CrossRuby.tool: unmatched platform: #{platform}"
       end) + name
@@ -77,8 +77,8 @@ def target_file_format
       "elf64-x86-64"
     when "x86-linux"
       "elf32-i386"
-    when "x86_64-darwin19"
-      "Mach-O 64-bit x86-64"
+    when "x86_64-darwin"
+      "Mach-O 64-bit x86-64" # hmm
     else
       raise "CrossRuby.target_file_format: unmatched platform: #{platform}"
     end
@@ -327,6 +327,10 @@ def verify_dll(dll, cross_ruby)
     ext.config_options << ENV['EXTOPTS']
     ext.cross_compile  = true
     ext.cross_platform = CROSS_RUBIES.map(&:platform).uniq
+    if RUBY_PLATFORM =~ /darwin/
+      # see test/test_gem_platform.rb for context
+      ext.platform = "x86_64-darwin"
+    end
     ext.cross_config_options << "--enable-cross-build"
     ext.cross_compiling do |spec|
       libs = dependencies.map { |name, dep| "#{name}-#{dep["version"]}" }.join(', ')