diff --git a/ballista/rust/core/src/serde/logical_plan/from_proto.rs b/ballista/rust/core/src/serde/logical_plan/from_proto.rs
index 020858fbfc3f..654386666488 100644
--- a/ballista/rust/core/src/serde/logical_plan/from_proto.rs
+++ b/ballista/rust/core/src/serde/logical_plan/from_proto.rs
@@ -976,7 +976,7 @@ impl TryInto<Expr> for &protobuf::LogicalExprNode {
 
                 Ok(Expr::AggregateFunction {
                     fun,
-                    args: vec![parse_required_expr(&expr.expr)?],
+                    arg: Box::new(parse_required_expr(&expr.expr)?),
                     distinct: false, //TODO
                 })
             }
diff --git a/ballista/rust/core/src/serde/logical_plan/to_proto.rs b/ballista/rust/core/src/serde/logical_plan/to_proto.rs
index 47e27483ff30..0d7b1e400978 100644
--- a/ballista/rust/core/src/serde/logical_plan/to_proto.rs
+++ b/ballista/rust/core/src/serde/logical_plan/to_proto.rs
@@ -1062,7 +1062,7 @@ impl TryInto<protobuf::LogicalExprNode> for &Expr {
                 })
             }
             Expr::AggregateFunction {
-                ref fun, ref args, ..
+                ref fun, ref arg, ..
             } => {
                 let aggr_function = match fun {
                     AggregateFunction::Min => protobuf::AggregateFunction::Min,
@@ -1072,7 +1072,7 @@ impl TryInto<protobuf::LogicalExprNode> for &Expr {
                     AggregateFunction::Count => protobuf::AggregateFunction::Count,
                 };
 
-                let arg = &args[0];
+                let arg = &**arg;
                 let aggregate_expr = Box::new(protobuf::AggregateExprNode {
                     aggr_function: aggr_function.into(),
                     expr: Some(Box::new(arg.try_into()?)),
diff --git a/ballista/rust/core/src/serde/physical_plan/from_proto.rs b/ballista/rust/core/src/serde/physical_plan/from_proto.rs
index d034f3ca3bfe..ced8a8d32208 100644
--- a/ballista/rust/core/src/serde/physical_plan/from_proto.rs
+++ b/ballista/rust/core/src/serde/physical_plan/from_proto.rs
@@ -325,10 +325,10 @@ impl TryInto<Arc<dyn ExecutionPlan>> for &protobuf::PhysicalPlanNode {
                 let df_planner = DefaultPhysicalPlanner::default();
                 for (expr, name) in &logical_agg_expr {
                     match expr {
-                        Expr::AggregateFunction { fun, args, .. } => {
+                        Expr::AggregateFunction { fun, arg, .. } => {
                             let arg = df_planner
                                 .create_physical_expr(
-                                    &args[0],
+                                    &**arg,
                                     &physical_schema,
                                     &ctx_state,
                                 )
diff --git a/datafusion/src/logical_plan/expr.rs b/datafusion/src/logical_plan/expr.rs
index 29723e73d25c..46c8bf84d1d0 100644
--- a/datafusion/src/logical_plan/expr.rs
+++ b/datafusion/src/logical_plan/expr.rs
@@ -187,7 +187,7 @@ pub enum Expr {
         /// Name of the function
         fun: aggregates::AggregateFunction,
         /// List of expressions to feed to the functions as arguments
-        args: Vec<Expr>,
+        arg: Box<Expr>,
         /// Whether this is a DISTINCT aggregation or not
         distinct: bool,
     },
@@ -259,12 +259,9 @@ impl Expr {
                     .collect::<Result<Vec<_>>>()?;
                 window_functions::return_type(fun, &data_types)
             }
-            Expr::AggregateFunction { fun, args, .. } => {
-                let data_types = args
-                    .iter()
-                    .map(|e| e.get_type(schema))
-                    .collect::<Result<Vec<_>>>()?;
-                aggregates::return_type(fun, &data_types)
+            Expr::AggregateFunction { fun, arg, .. } => {
+                let data_type = arg.get_type(schema)?;
+                aggregates::return_type(fun, &[data_type])
             }
             Expr::AggregateUDF { fun, args, .. } => {
                 let data_types = args
@@ -590,9 +587,7 @@ impl Expr {
             Expr::WindowFunction { args, .. } => args
                 .iter()
                 .try_fold(visitor, |visitor, arg| arg.accept(visitor)),
-            Expr::AggregateFunction { args, .. } => args
-                .iter()
-                .try_fold(visitor, |visitor, arg| arg.accept(visitor)),
+            Expr::AggregateFunction { arg, .. } => arg.accept(visitor),
             Expr::AggregateUDF { args, .. } => args
                 .iter()
                 .try_fold(visitor, |visitor, arg| arg.accept(visitor)),
@@ -728,11 +723,11 @@ impl Expr {
                 fun,
             },
             Expr::AggregateFunction {
-                args,
+                arg,
                 fun,
                 distinct,
             } => Expr::AggregateFunction {
-                args: rewrite_vec(args, rewriter)?,
+                arg: rewrite_boxed(arg, rewriter)?,
                 fun,
                 distinct,
             },
@@ -969,7 +964,7 @@ pub fn min(expr: Expr) -> Expr {
     Expr::AggregateFunction {
         fun: aggregates::AggregateFunction::Min,
         distinct: false,
-        args: vec![expr],
+        arg: Box::new(expr),
     }
 }
 
@@ -978,7 +973,7 @@ pub fn max(expr: Expr) -> Expr {
     Expr::AggregateFunction {
         fun: aggregates::AggregateFunction::Max,
         distinct: false,
-        args: vec![expr],
+        arg: Box::new(expr),
     }
 }
 
@@ -987,7 +982,7 @@ pub fn sum(expr: Expr) -> Expr {
     Expr::AggregateFunction {
         fun: aggregates::AggregateFunction::Sum,
         distinct: false,
-        args: vec![expr],
+        arg: Box::new(expr),
     }
 }
 
@@ -996,7 +991,7 @@ pub fn avg(expr: Expr) -> Expr {
     Expr::AggregateFunction {
         fun: aggregates::AggregateFunction::Avg,
         distinct: false,
-        args: vec![expr],
+        arg: Box::new(expr),
     }
 }
 
@@ -1005,7 +1000,7 @@ pub fn count(expr: Expr) -> Expr {
     Expr::AggregateFunction {
         fun: aggregates::AggregateFunction::Count,
         distinct: false,
-        args: vec![expr],
+        arg: Box::new(expr),
     }
 }
 
@@ -1014,7 +1009,7 @@ pub fn count_distinct(expr: Expr) -> Expr {
     Expr::AggregateFunction {
         fun: aggregates::AggregateFunction::Count,
         distinct: true,
-        args: vec![expr],
+        arg: Box::new(expr),
     }
 }
 
@@ -1276,9 +1271,9 @@ impl fmt::Debug for Expr {
             Expr::AggregateFunction {
                 fun,
                 distinct,
-                ref args,
+                ref arg,
                 ..
-            } => fmt_function(f, &fun.to_string(), *distinct, args),
+            } => fmt_function(f, &fun.to_string(), *distinct, &[*arg.clone()]),
             Expr::AggregateUDF { fun, ref args, .. } => {
                 fmt_function(f, &fun.name, false, args)
             }
@@ -1394,9 +1389,9 @@ fn create_name(e: &Expr, input_schema: &DFSchema) -> Result<String> {
         Expr::AggregateFunction {
             fun,
             distinct,
-            args,
+            arg,
             ..
-        } => create_function_name(&fun.to_string(), *distinct, args, input_schema),
+        } => create_function_name(&fun.to_string(), *distinct, &[*arg.clone()], input_schema),
         Expr::AggregateUDF { fun, args } => {
             let mut names = Vec::with_capacity(args.len());
             for e in args {
diff --git a/datafusion/src/optimizer/utils.rs b/datafusion/src/optimizer/utils.rs
index 284ead252ac6..ae315090fee9 100644
--- a/datafusion/src/optimizer/utils.rs
+++ b/datafusion/src/optimizer/utils.rs
@@ -266,7 +266,7 @@ pub fn expr_sub_expressions(expr: &Expr) -> Result<Vec<Expr>> {
         Expr::ScalarFunction { args, .. } => Ok(args.clone()),
         Expr::ScalarUDF { args, .. } => Ok(args.clone()),
         Expr::WindowFunction { args, .. } => Ok(args.clone()),
-        Expr::AggregateFunction { args, .. } => Ok(args.clone()),
+        Expr::AggregateFunction { arg, .. } => Ok(vec![arg.as_ref().to_owned()]),
         Expr::AggregateUDF { args, .. } => Ok(args.clone()),
         Expr::Case {
             expr,
@@ -344,7 +344,7 @@ pub fn rewrite_expression(expr: &Expr, expressions: &[Expr]) -> Result<Expr> {
         }),
         Expr::AggregateFunction { fun, distinct, .. } => Ok(Expr::AggregateFunction {
             fun: fun.clone(),
-            args: expressions.to_vec(),
+            arg: Box::new(expressions[0].clone()),
             distinct: *distinct,
         }),
         Expr::AggregateUDF { fun, .. } => Ok(Expr::AggregateUDF {
diff --git a/datafusion/src/physical_plan/planner.rs b/datafusion/src/physical_plan/planner.rs
index 7ddfaf8f6897..49863ec78f73 100644
--- a/datafusion/src/physical_plan/planner.rs
+++ b/datafusion/src/physical_plan/planner.rs
@@ -779,19 +779,14 @@ impl DefaultPhysicalPlanner {
             Expr::AggregateFunction {
                 fun,
                 distinct,
-                args,
+                arg,
                 ..
             } => {
-                let args = args
-                    .iter()
-                    .map(|e| {
-                        self.create_physical_expr(e, physical_input_schema, ctx_state)
-                    })
-                    .collect::<Result<Vec<_>>>()?;
+                let args = self.create_physical_expr(arg, physical_input_schema, ctx_state)?;
                 aggregates::create_aggregate_expr(
                     fun,
                     *distinct,
-                    &args,
+                    &[args],
                     physical_input_schema,
                     name,
                 )
diff --git a/datafusion/src/sql/planner.rs b/datafusion/src/sql/planner.rs
index a3027e589985..9c41dc0292f5 100644
--- a/datafusion/src/sql/planner.rs
+++ b/datafusion/src/sql/planner.rs
@@ -1136,7 +1136,7 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
                     return Ok(Expr::AggregateFunction {
                         fun,
                         distinct: function.distinct,
-                        args,
+                        arg: Box::new(args[0].clone()),
                     });
                 };
 
diff --git a/datafusion/src/sql/utils.rs b/datafusion/src/sql/utils.rs
index 70b9df060839..84df5bdf87c5 100644
--- a/datafusion/src/sql/utils.rs
+++ b/datafusion/src/sql/utils.rs
@@ -215,14 +215,11 @@ where
         None => match expr {
             Expr::AggregateFunction {
                 fun,
-                args,
+                arg,
                 distinct,
             } => Ok(Expr::AggregateFunction {
                 fun: fun.clone(),
-                args: args
-                    .iter()
-                    .map(|e| clone_with_replacement(e, replacement_fn))
-                    .collect::<Result<Vec<Expr>>>()?,
+                arg: Box::new(clone_with_replacement(arg, replacement_fn)?),
                 distinct: *distinct,
             }),
             Expr::WindowFunction { fun, args } => Ok(Expr::WindowFunction {