diff --git a/executor/analyze_test.go b/executor/analyze_test.go
index addb97d5c1482..5ea14b6ac0c8e 100644
--- a/executor/analyze_test.go
+++ b/executor/analyze_test.go
@@ -310,6 +310,8 @@ func (s *testFastAnalyze) TestFastAnalyze(c *C) {
 
 	// Test CM Sketch built from fast analyze.
 	tk.MustExec("create table t1(a int, b int, index idx(a, b))")
+	// Should not panic.
+	tk.MustExec("analyze table t1")
 	tk.MustExec("insert into t1 values (1,1),(1,1),(1,2),(1,2)")
 	tk.MustExec("analyze table t1")
 	tk.MustQuery("explain select a from t1 where a = 1").Check(testkit.Rows(
diff --git a/statistics/cmsketch.go b/statistics/cmsketch.go
index 554300635f185..f97e0860426fa 100644
--- a/statistics/cmsketch.go
+++ b/statistics/cmsketch.go
@@ -336,6 +336,9 @@ func (c *CMSketch) mergeTopN(lTopN map[uint64][]*TopNMeta, rTopN map[uint64][]*T
 
 // MergeCMSketch merges two CM Sketch.
 func (c *CMSketch) MergeCMSketch(rc *CMSketch, numTopN uint32) error {
+	if c == nil || rc == nil {
+		return nil
+	}
 	if c.depth != rc.depth || c.width != rc.width {
 		return errors.New("Dimensions of Count-Min Sketch should be the same")
 	}