diff --git a/datafusion/optimizer/src/single_distinct_to_groupby.rs b/datafusion/optimizer/src/single_distinct_to_groupby.rs
index 1769314ebc0c..a4d6619f2a4f 100644
--- a/datafusion/optimizer/src/single_distinct_to_groupby.rs
+++ b/datafusion/optimizer/src/single_distinct_to_groupby.rs
@@ -83,7 +83,7 @@ fn optimize(plan: &LogicalPlan) -> Result<LogicalPlan> {
                             Expr::AggregateFunction {
                                 fun: fun.clone(),
                                 args: vec![col(SINGLE_DISTINCT_ALIAS)],
-                                distinct: false,
+                                distinct: false, // intentional to remove distict here
                             }
                         }
                         _ => agg_expr.clone(),
diff --git a/datafusion/proto/proto/datafusion.proto b/datafusion/proto/proto/datafusion.proto
index 7b08e4f40456..0b4a43e83e71 100644
--- a/datafusion/proto/proto/datafusion.proto
+++ b/datafusion/proto/proto/datafusion.proto
@@ -474,6 +474,7 @@ enum AggregateFunction {
 message AggregateExprNode {
   AggregateFunction aggr_function = 1;
   repeated LogicalExprNode expr = 2;
+  bool distinct = 3;
 }
 
 message AggregateUDFExprNode {
diff --git a/datafusion/proto/src/from_proto.rs b/datafusion/proto/src/from_proto.rs
index 63d9fe2b79c0..12f94ce3620e 100644
--- a/datafusion/proto/src/from_proto.rs
+++ b/datafusion/proto/src/from_proto.rs
@@ -890,7 +890,7 @@ pub fn parse_expr(
                     .iter()
                     .map(|e| parse_expr(e, registry))
                     .collect::<Result<Vec<_>, _>>()?,
-                distinct: false, // TODO
+                distinct: expr.distinct,
             })
         }
         ExprType::Alias(alias) => Ok(Expr::Alias(
diff --git a/datafusion/proto/src/lib.rs b/datafusion/proto/src/lib.rs
index eecca1b6ad59..c843de630289 100644
--- a/datafusion/proto/src/lib.rs
+++ b/datafusion/proto/src/lib.rs
@@ -912,6 +912,28 @@ mod roundtrip_tests {
         roundtrip_expr_test(test_expr, ctx);
     }
 
+    #[test]
+    fn roundtrip_count() {
+        let test_expr = Expr::AggregateFunction {
+            fun: AggregateFunction::Count,
+            args: vec![col("bananas")],
+            distinct: false,
+        };
+        let ctx = SessionContext::new();
+        roundtrip_expr_test(test_expr, ctx);
+    }
+
+    #[test]
+    fn roundtrip_count_distinct() {
+        let test_expr = Expr::AggregateFunction {
+            fun: AggregateFunction::Count,
+            args: vec![col("bananas")],
+            distinct: true,
+        };
+        let ctx = SessionContext::new();
+        roundtrip_expr_test(test_expr, ctx);
+    }
+
     #[test]
     fn roundtrip_approx_percentile_cont() {
         let test_expr = Expr::AggregateFunction {
diff --git a/datafusion/proto/src/to_proto.rs b/datafusion/proto/src/to_proto.rs
index a022769dcab1..d3f68b3b4276 100644
--- a/datafusion/proto/src/to_proto.rs
+++ b/datafusion/proto/src/to_proto.rs
@@ -502,7 +502,9 @@ impl TryFrom<&Expr> for protobuf::LogicalExprNode {
                 }
             }
             Expr::AggregateFunction {
-                ref fun, ref args, ..
+                ref fun,
+                ref args,
+                ref distinct,
             } => {
                 let aggr_function = match fun {
                     AggregateFunction::ApproxDistinct => {
@@ -550,6 +552,7 @@ impl TryFrom<&Expr> for protobuf::LogicalExprNode {
                         .iter()
                         .map(|v| v.try_into())
                         .collect::<Result<Vec<_>, _>>()?,
+                    distinct: *distinct,
                 };
                 Self {
                     expr_type: Some(ExprType::AggregateExpr(aggregate_expr)),