diff --git a/mysql-test/r/merge.result b/mysql-test/r/merge.result
index bf9108459d7..934085ab796 100644
--- a/mysql-test/r/merge.result
+++ b/mysql-test/r/merge.result
@@ -2141,4 +2141,24 @@ SELECT * FROM m1;
 c1
 DROP TABLE m1;
 DROP TABLE t1;
+#
+# Bug45781 infinite hang/crash in "opening tables" after handler tries to
+#          open merge table
+#
+DROP TABLE IF EXISTS m1,t1;
+CREATE TABLE t1(a int)engine=myisam;
+CREATE TABLE t2(a int)engine=myisam;
+CREATE TABLE t3(a int)engine=myisam;
+CREATE TABLE t4(a int)engine=myisam;
+CREATE TABLE t5(a int)engine=myisam;
+CREATE TABLE t6(a int)engine=myisam;
+CREATE TABLE t7(a int)engine=myisam;
+CREATE TABLE m1(a int)engine=merge union=(t1,t2,t3,t4,t5,t6,t7);
+SELECT 1 FROM m1;
+1
+HANDLER m1 OPEN;
+ERROR HY000: Table storage engine for 'm1' doesn't have this option
+DROP TABLE m1,t1,t2,t3,t4,t5,t6,t7;
+SELECT 1 FROM m1;
+ERROR 42S02: Table 'test.m1' doesn't exist
 End of 5.1 tests
diff --git a/mysql-test/t/merge.test b/mysql-test/t/merge.test
index 8760876b7ee..0d90468fc8d 100644
--- a/mysql-test/t/merge.test
+++ b/mysql-test/t/merge.test
@@ -1555,4 +1555,28 @@ SELECT * FROM m1;
 DROP TABLE m1;
 DROP TABLE t1;
 
+--echo #
+--echo # Bug45781 infinite hang/crash in "opening tables" after handler tries to
+--echo #          open merge table
+--echo #
+
+--disable_warnings
+DROP TABLE IF EXISTS m1,t1;
+--enable_warnings
+
+CREATE TABLE t1(a int)engine=myisam;
+CREATE TABLE t2(a int)engine=myisam;
+CREATE TABLE t3(a int)engine=myisam;
+CREATE TABLE t4(a int)engine=myisam;
+CREATE TABLE t5(a int)engine=myisam;
+CREATE TABLE t6(a int)engine=myisam;
+CREATE TABLE t7(a int)engine=myisam;
+CREATE TABLE m1(a int)engine=merge union=(t1,t2,t3,t4,t5,t6,t7);
+SELECT 1 FROM m1;
+--error ER_ILLEGAL_HA
+HANDLER m1 OPEN;
+DROP TABLE m1,t1,t2,t3,t4,t5,t6,t7;
+--error ER_NO_SUCH_TABLE
+SELECT 1 FROM m1; # Should not hang!
+
 --echo End of 5.1 tests
diff --git a/sql/sql_handler.cc b/sql/sql_handler.cc
index 16810e29343..1e92d95573a 100644
--- a/sql/sql_handler.cc
+++ b/sql/sql_handler.cc
@@ -252,14 +252,37 @@ bool mysql_ha_open(THD *thd, TABLE_LIST *tables, bool reopen)
 
   /* for now HANDLER can be used only for real TABLES */
   tables->required_type= FRMTYPE_TABLE;
+  /*
+    We use open_tables() here, rather than, say,
+    open_ltable() or open_table() because we would like to be able
+    to open a temporary table.
+  */
   error= open_tables(thd, &tables, &counter, 0);
-  /* restore the state and merge the opened table into handler_tables list */
   if (thd->open_tables)
   {
-    thd->open_tables->next= thd->handler_tables;
-    thd->handler_tables= thd->open_tables;
+    if (thd->open_tables->next)
+    {
+      /*
+        We opened something that is more than a single table.
+        This happens with MERGE engine. Don't try to link
+        this mess into thd->handler_tables list, close it
+        and report an error. We must do it right away
+        because mysql_ha_close_table(), called down the road,
+        can close a single table only.
+      */
+      close_thread_tables(thd);
+      my_error(ER_ILLEGAL_HA, MYF(0), tables->alias);
+      error= 1;
+    }
+    else
+    {
+      /* Merge the opened table into handler_tables list. */
+      thd->open_tables->next= thd->handler_tables;
+      thd->handler_tables= thd->open_tables;
+    }
   }
 
+  /* Restore the state. */
   thd->open_tables= backup_open_tables;
 
   if (error)