diff --git a/mysql-test/r/variables-big.result b/mysql-test/r/variables-big.result
new file mode 100644
index 00000000000..d7906869276
--- /dev/null
+++ b/mysql-test/r/variables-big.result
@@ -0,0 +1,20 @@
+set session transaction_prealloc_size=1024*1024*1024*1;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*2;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	2	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*3;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*4;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*5;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist
diff --git a/mysql-test/t/variables-big.test b/mysql-test/t/variables-big.test
new file mode 100644
index 00000000000..43326f3d016
--- /dev/null
+++ b/mysql-test/t/variables-big.test
@@ -0,0 +1,20 @@
+#
+# test variables big
+#
+
+--source include/big_test.inc
+
+#
+# Bug #27322  	failure to allocate transaction_prealloc_size causes crash
+#
+
+set session transaction_prealloc_size=1024*1024*1024*1;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*2;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*3;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*4;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*5;
+show processlist;
diff --git a/mysys/my_alloc.c b/mysys/my_alloc.c
index 5a0ac7b87f7..233abf793e0 100644
--- a/mysys/my_alloc.c
+++ b/mysys/my_alloc.c
@@ -133,6 +133,10 @@ void reset_root_defaults(MEM_ROOT *mem_root, uint block_size,
         mem->next= *prev;
         *prev= mem_root->pre_alloc= mem; 
       }
+      else
+      {
+        mem_root->pre_alloc= 0;
+      }
     }
   }
   else