diff --git a/mysql-test/suite/rpl/r/rpl_heartbeat_basic.result b/mysql-test/suite/rpl/r/rpl_heartbeat_basic.result
index a9bd16cc85ad2..ee4cfd4129071 100644
--- a/mysql-test/suite/rpl/r/rpl_heartbeat_basic.result
+++ b/mysql-test/suite/rpl/r/rpl_heartbeat_basic.result
@@ -182,6 +182,18 @@ CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=MASTER_PORT, MASTER_USER='
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '''' at line 1
 RESET SLAVE;
 
+*** MDEV-38454: MASTER_HEARTBEAT_PERIOD should accept + sign ***
+CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=MASTER_PORT, MASTER_USER='root', MASTER_CONNECT_RETRY=20, MASTER_HEARTBEAT_PERIOD=+60;
+SHOW GLOBAL STATUS LIKE 'slave_heartbeat_period';
+Variable_name	Value
+Slave_heartbeat_period	60.000
+RESET SLAVE;
+CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=MASTER_PORT, MASTER_USER='root', MASTER_CONNECT_RETRY=20, MASTER_HEARTBEAT_PERIOD=60;
+SHOW GLOBAL STATUS LIKE 'slave_heartbeat_period';
+Variable_name	Value
+Slave_heartbeat_period	60.000
+RESET SLAVE;
+
 *** Running slave ***
 CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=MASTER_PORT, MASTER_USER='root', MASTER_CONNECT_RETRY=20, MASTER_HEARTBEAT_PERIOD=0.1;
 include/start_slave.inc
diff --git a/mysql-test/suite/rpl/t/rpl_heartbeat_basic.test b/mysql-test/suite/rpl/t/rpl_heartbeat_basic.test
index fb67ad770d57a..3cfcbf5ed2864 100644
--- a/mysql-test/suite/rpl/t/rpl_heartbeat_basic.test
+++ b/mysql-test/suite/rpl/t/rpl_heartbeat_basic.test
@@ -238,6 +238,22 @@ eval CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=$MASTER_MYPORT, MASTE
 RESET SLAVE;
 --echo
 
+#
+# MDEV-38454: MASTER_HEARTBEAT_PERIOD should accept values with + sign
+#
+--echo *** MDEV-38454: MASTER_HEARTBEAT_PERIOD should accept + sign ***
+# Test with + sign (was broken before fix)
+--replace_result $MASTER_MYPORT MASTER_PORT
+eval CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=$MASTER_MYPORT, MASTER_USER='root', MASTER_CONNECT_RETRY=$connect_retry, MASTER_HEARTBEAT_PERIOD=+60;
+SHOW GLOBAL STATUS LIKE 'slave_heartbeat_period';
+RESET SLAVE;
+# Test without + sign (should still work)
+--replace_result $MASTER_MYPORT MASTER_PORT
+eval CHANGE MASTER TO MASTER_HOST='127.0.0.1', MASTER_PORT=$MASTER_MYPORT, MASTER_USER='root', MASTER_CONNECT_RETRY=$connect_retry, MASTER_HEARTBEAT_PERIOD=60;
+SHOW GLOBAL STATUS LIKE 'slave_heartbeat_period';
+RESET SLAVE;
+--echo
+
 #
 # Testing heartbeat 
 #
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 9d2d6a8f4a395..67eaa221b8ac2 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -2265,9 +2265,9 @@ master_def:
             Lex->mi.ssl_crlpath= $3.str;
           }
 
-        | MASTER_HEARTBEAT_PERIOD_SYM '=' NUM_literal
+        | MASTER_HEARTBEAT_PERIOD_SYM '=' opt_plus NUM_literal
           {
-            Lex->mi.heartbeat_period= (float) $3->val_real();
+            Lex->mi.heartbeat_period= (float) $4->val_real();
             if (unlikely(Lex->mi.heartbeat_period >
                          SLAVE_MAX_HEARTBEAT_PERIOD) ||
                 unlikely(Lex->mi.heartbeat_period < 0.0))