diff --git a/rubygem-mysql2.spec b/rubygem-mysql2.spec
index 0b459d3..cd2c37e 100644
--- a/rubygem-mysql2.spec
+++ b/rubygem-mysql2.spec
@@ -86,7 +86,9 @@ pushd .%{gem_instdir}
 
 TOP_DIR=$(pwd)
 # Use testing port because the standard mysqld port 3306 is occupied.
-MYSQL_TEST_PORT="13306"
+# Assign a random port to consider a case of multi builds in parallel in a host.
+# https://src.fedoraproject.org/rpms/rubygem-pg/pull-request/3
+MYSQL_TEST_PORT="$((13306 + ${RANDOM} % 1000))"
 MYSQL_TEST_USER=$(id -un)
 MYSQL_TEST_DATA_DIR="${TOP_DIR}/data"
 MYSQL_TEST_SOCKET="${TOP_DIR}/mysql.sock"