diff --git a/.ci/build.sh b/.ci/build.sh
index da4169516..278e252d8 100644
--- a/.ci/build.sh
+++ b/.ci/build.sh
@@ -59,13 +59,14 @@ make_tar() {
 			sudo apt-get clean
 		elif which port > /dev/null 2>&1
 		then
+			sudo port selfupdate
 			sudo port install gnutar xz
 		fi
 	fi
-	
-	# Prefer gnutar on macOS.
+
+	# Use MacPorts gnutar (if installed) on macOS.
 	local tar_cmd=tar
-	which gnutar > /dev/null 2>&1 && tar_cmd=gnutar
+	which gnutar > /dev/null 2>&1 && local tar_cmd=gnutar
 
 	# Determine the best supported compression type.
 	local compression_flag=