diff --git a/statistics/index.go b/statistics/index.go
index a8c39da22b637..257e6ff488963 100644
--- a/statistics/index.go
+++ b/statistics/index.go
@@ -240,8 +240,10 @@ func (idx *Index) GetRowCount(sctx sessionctx.Context, coll *HistColl, indexRang
 			if fullLen {
 				// At most 1 in this case.
 				if idx.Info.Unique {
-					totalCount++
-					continue
+					if !indexRange.IsOnlyNull() {
+						totalCount++
+						continue
+					}
 				}
 				count = idx.equalRowCount(lb, realtimeRowCount)
 				// If the current table row count has changed, we should scale the row count accordingly.
diff --git a/statistics/integration_test.go b/statistics/integration_test.go
index 0493d870aec89..6adb1008b490d 100644
--- a/statistics/integration_test.go
+++ b/statistics/integration_test.go
@@ -808,3 +808,18 @@ func TestIssue49986(t *testing.T) {
 			"        └─Selection 10.00 cop[tikv]  eq(\"astp2019121731703151\", test.acc.m)",
 			"          └─TableFullScan 10000.00 cop[tikv] table:b keep order:false, stats:pseudo"))
 }
+
+func TestIssue56116(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+
+	tk.MustExec("create table t2(id bigint(20) DEFAULT NULL, UNIQUE KEY index_on_id (id))")
+	tk.MustExec("insert into t2 values (), (), ()")
+	tk.MustExec("analyze table t2")
+	tk.MustQuery("explain select count(*) from t2 where id is null;").Check(testkit.Rows(
+		"StreamAgg_17 1.00 root  funcs:count(Column#5)->Column#3",
+		"└─IndexReader_18 1.00 root  index:StreamAgg_9",
+		"  └─StreamAgg_9 1.00 cop[tikv]  funcs:count(1)->Column#5",
+		"    └─IndexRangeScan_16 3.00 cop[tikv] table:t2, index:index_on_id(id) range:[NULL,NULL], keep order:false"))
+}
diff --git a/util/ranger/types.go b/util/ranger/types.go
index 6c6ab98c52157..6589d42e7e884 100644
--- a/util/ranger/types.go
+++ b/util/ranger/types.go
@@ -126,6 +126,18 @@ func (ran *Range) isPoint(stmtCtx *stmtctx.StatementContext, regardNullAsPoint b
 	return !ran.LowExclude && !ran.HighExclude
 }
 
+// IsOnlyNull checks if the range has [NULL, NULL] or [NULL NULL, NULL NULL] range.
+func (ran *Range) IsOnlyNull() bool {
+	for i := range ran.LowVal {
+		a := ran.LowVal[i]
+		b := ran.HighVal[i]
+		if !(a.IsNull() && b.IsNull()) {
+			return false
+		}
+	}
+	return true
+}
+
 // IsPointNonNullable returns if the range is a point without NULL.
 func (ran *Range) IsPointNonNullable(sctx sessionctx.Context) bool {
 	return ran.isPoint(sctx.GetSessionVars().StmtCtx, false)