diff --git a/e2e_test/udf/bug_fixes/17560_udaf_as_win_func.slt b/e2e_test/udf/bug_fixes/17560_udaf_as_win_func.slt
new file mode 100644
index 0000000000000..3d8e3279a8b42
--- /dev/null
+++ b/e2e_test/udf/bug_fixes/17560_udaf_as_win_func.slt
@@ -0,0 +1,19 @@
+# https://github.com/risingwavelabs/risingwave/issues/17560
+
+statement ok
+create aggregate sum00(value int) returns int language python as $$
+def create_state():
+    return 0
+def accumulate(state, value):
+    return state + value
+def retract(state, value):
+    return state - value
+def finish(state):
+    return state
+$$;
+
+query ii
+select t.value, sum00(weight) OVER (PARTITION BY value) from (values (1, 1), (null, 2), (3, 3)) as t(value, weight);
+----
+1 1
+3 3
diff --git a/src/frontend/src/expr/window_function.rs b/src/frontend/src/expr/window_function.rs
index 70f6a79866fb3..8f2e6c66728dd 100644
--- a/src/frontend/src/expr/window_function.rs
+++ b/src/frontend/src/expr/window_function.rs
@@ -16,11 +16,11 @@ use itertools::Itertools;
 use risingwave_common::bail_not_implemented;
 use risingwave_common::types::DataType;
 use risingwave_expr::aggregate::AggKind;
-use risingwave_expr::sig::FUNCTION_REGISTRY;
 use risingwave_expr::window_function::{Frame, WindowFuncKind};
 
 use super::{Expr, ExprImpl, OrderBy, RwResult};
 use crate::error::{ErrorCode, RwError};
+use crate::expr::infer_type;
 
 /// A window function performs a calculation across a set of table rows that are somehow related to
 /// the current row, according to the window spec `OVER (PARTITION BY .. ORDER BY ..)`.
@@ -45,10 +45,10 @@ impl WindowFunction {
         kind: WindowFuncKind,
         partition_by: Vec<ExprImpl>,
         order_by: OrderBy,
-        args: Vec<ExprImpl>,
+        mut args: Vec<ExprImpl>,
         frame: Option<Frame>,
     ) -> RwResult<Self> {
-        let return_type = Self::infer_return_type(&kind, &args)?;
+        let return_type = Self::infer_return_type(&kind, &mut args)?;
         Ok(Self {
             kind,
             args,
@@ -59,7 +59,7 @@ impl WindowFunction {
         })
     }
 
-    fn infer_return_type(kind: &WindowFuncKind, args: &[ExprImpl]) -> RwResult<DataType> {
+    fn infer_return_type(kind: &WindowFuncKind, args: &mut [ExprImpl]) -> RwResult<DataType> {
         use WindowFuncKind::*;
         match (kind, args) {
             (RowNumber, []) => Ok(DataType::Int64),
@@ -87,13 +87,13 @@ impl WindowFunction {
                 );
             }
 
-            (Aggregate(AggKind::Builtin(agg_kind)), args) => {
-                let arg_types = args.iter().map(ExprImpl::return_type).collect::<Vec<_>>();
-                let return_type = FUNCTION_REGISTRY.get_return_type(*agg_kind, &arg_types)?;
-                Ok(return_type)
-            }
+            (Aggregate(agg_kind), args) => Ok(match agg_kind {
+                AggKind::Builtin(kind) => infer_type((*kind).into(), args)?,
+                AggKind::UserDefined(udf) => udf.return_type.as_ref().unwrap().into(),
+                AggKind::WrapScalar(expr) => expr.return_type.as_ref().unwrap().into(),
+            }),
 
-            _ => {
+            (_, args) => {
                 let args = args
                     .iter()
                     .map(|e| format!("{}", e.return_type()))