diff --git a/_build.sh b/_build.sh
index 96a0fca61..d94fdb047 100755
--- a/_build.sh
+++ b/_build.sh
@@ -754,9 +754,9 @@ build_single_target() {
     if [ "${_HOSTOS}" != "${_OS}" ]; then
       _CMAKE_GLOBAL="-DCMAKE_SYSTEM_NAME=Darwin ${_CMAKE_GLOBAL}"
     fi
-    # macOS 10.13 High Sierra 2017-09-25. Seems to work for arm64 builds,
+    # macOS 10.9 Mavericks 2013-10-22. Seems to work for arm64 builds,
     # though arm64 was released in macOS 11.0 Big Sur 2020-11-12.
-    macminver='10.13'
+    macminver='10.9'
     _CMAKE_GLOBAL="${_CMAKE_GLOBAL} -DCMAKE_OSX_DEPLOYMENT_TARGET=${macminver}"
     _CFLAGS_GLOBAL="${_CFLAGS_GLOBAL} -mmacosx-version-min=${macminver}"
     _CXXFLAGS_GLOBAL="${_CXXFLAGS_GLOBAL} -mmacosx-version-min=${macminver}"