diff --git a/executor/aggfuncs/func_cume_dist.go b/executor/aggfuncs/func_cume_dist.go
index e727abfac9..39d7c30221 100644
--- a/executor/aggfuncs/func_cume_dist.go
+++ b/executor/aggfuncs/func_cume_dist.go
@@ -14,10 +14,17 @@
 package aggfuncs
 
 import (
+	"unsafe"
+
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/util/chunk"
 )
 
+const (
+	// DefPartialResult4CumeDistSize is the size of partialResult4CumeDist
+	DefPartialResult4CumeDistSize = int64(unsafe.Sizeof(partialResult4CumeDist{}))
+)
+
 type cumeDist struct {
 	baseAggFunc
 	rowComparer
@@ -30,7 +37,7 @@ type partialResult4CumeDist struct {
 }
 
 func (r *cumeDist) AllocPartialResult() (pr PartialResult, memDelta int64) {
-	return PartialResult(&partialResult4CumeDist{}), 0
+	return PartialResult(&partialResult4CumeDist{}), DefPartialResult4CumeDistSize
 }
 
 func (r *cumeDist) ResetPartialResult(pr PartialResult) {
@@ -43,7 +50,8 @@ func (r *cumeDist) ResetPartialResult(pr PartialResult) {
 func (r *cumeDist) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) (memDelta int64, err error) {
 	p := (*partialResult4CumeDist)(pr)
 	p.rows = append(p.rows, rowsInGroup...)
-	return 0, nil
+	memDelta += int64(len(rowsInGroup)) * DefRowSize
+	return memDelta, nil
 }
 
 func (r *cumeDist) AppendFinalResult2Chunk(sctx sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
diff --git a/executor/aggfuncs/func_cume_dist_test.go b/executor/aggfuncs/func_cume_dist_test.go
new file mode 100644
index 0000000000..b236f531f2
--- /dev/null
+++ b/executor/aggfuncs/func_cume_dist_test.go
@@ -0,0 +1,35 @@
+// Copyright 2020 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aggfuncs_test
+
+import (
+	. "github.com/pingcap/check"
+	"github.com/pingcap/parser/ast"
+	"github.com/pingcap/parser/mysql"
+	"github.com/pingcap/tidb/executor/aggfuncs"
+)
+
+func (s *testSuite) TestMemCumeDist(c *C) {
+	tests := []windowMemTest{
+		buildWindowMemTester(ast.WindowFuncCumeDist, mysql.TypeLonglong, 0, 1, 1,
+			aggfuncs.DefPartialResult4CumeDistSize, rowMemDeltaGens),
+		buildWindowMemTester(ast.WindowFuncCumeDist, mysql.TypeLonglong, 0, 2, 0,
+			aggfuncs.DefPartialResult4CumeDistSize, rowMemDeltaGens),
+		buildWindowMemTester(ast.WindowFuncCumeDist, mysql.TypeLonglong, 0, 4, 1,
+			aggfuncs.DefPartialResult4CumeDistSize, rowMemDeltaGens),
+	}
+	for _, test := range tests {
+		s.testWindowAggMemFunc(c, test)
+	}
+}