diff --git a/e2e_test/batch/catalog/pg_cast.slt.part b/e2e_test/batch/catalog/pg_cast.slt.part
index b8ab68a5ed5cd..b1558d1e144c4 100644
--- a/e2e_test/batch/catalog/pg_cast.slt.part
+++ b/e2e_test/batch/catalog/pg_cast.slt.part
@@ -82,8 +82,9 @@ SELECT * FROM pg_catalog.pg_cast;
 78 3802 701 e
 79 3802 1700 e
 80 3802 1043 a
-81 1301 701 e
-82 1301 1043 a
+81 20 20 e
+82 1301 701 e
+83 1301 1043 a
 
 query TT rowsort
 SELECT s.typname, t.typname
diff --git a/src/common/src/types/serial.rs b/src/common/src/types/serial.rs
index 9bfbf5e4fcac7..5c84c95fa0f7a 100644
--- a/src/common/src/types/serial.rs
+++ b/src/common/src/types/serial.rs
@@ -26,6 +26,12 @@ use crate::util::row_id::RowId;
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Ord, PartialOrd, Default, Hash)]
 pub struct Serial(i64);
 
+impl From<Serial> for i64 {
+    fn from(value: Serial) -> i64 {
+        value.0
+    }
+}
+
 impl From<i64> for Serial {
     fn from(value: i64) -> Self {
         Self(value)
diff --git a/src/expr/impl/src/scalar/cast.rs b/src/expr/impl/src/scalar/cast.rs
index dc81e3ab77bac..bf8afc7712f93 100644
--- a/src/expr/impl/src/scalar/cast.rs
+++ b/src/expr/impl/src/scalar/cast.rs
@@ -87,6 +87,7 @@ pub fn jsonb_to_number<T: TryFrom<F64>>(v: JsonbRef<'_>) -> Result<T> {
 #[function("cast(int4) -> int2")]
 #[function("cast(int8) -> int2")]
 #[function("cast(int8) -> int4")]
+#[function("cast(serial) -> int8")]
 #[function("cast(float4) -> int2")]
 #[function("cast(float8) -> int2")]
 #[function("cast(float4) -> int4")]
diff --git a/src/frontend/src/expr/type_inference/cast.rs b/src/frontend/src/expr/type_inference/cast.rs
index aa7e1c8ee9192..1f1a96e92b826 100644
--- a/src/frontend/src/expr/type_inference/cast.rs
+++ b/src/frontend/src/expr/type_inference/cast.rs
@@ -216,22 +216,23 @@ pub static CAST_MAP: LazyLock<CastMap> = LazyLock::new(|| {
     use DataTypeName::*;
     const CAST_TABLE: &[(&str, DataTypeName)] = &[
         // 123456789ABCDEF
-        (". e            a", Boolean),     // 0
-        (" .iiiiii       a", Int16),       // 1
-        ("ea.iiiii       a", Int32),       // 2
-        (" aa.iiii       a", Int64),       // 3
-        (" aaa.ii        a", Decimal),     // 4
-        (" aaaa.i        a", Float32),     // 5
-        (" aaaaa.        a", Float64),     // 6
-        ("      e.       a", Int256),      // 7
-        ("        .ii    a", Date),        // 8
-        ("        a.ia   a", Timestamp),   // 9
-        ("        aa.a   a", Timestamptz), // A
-        ("           .i  a", Time),        // B
-        ("           a.  a", Interval),    // C
-        ("eeeeeee      . a", Jsonb),       // D
-        ("              .a", Bytea),       // E
-        ("eeeeeeeeeeeeeee.", Varchar),     // F
+        (". e            a ", Boolean),     // 0
+        (" .iiiiii       a ", Int16),       // 1
+        ("ea.iiiii       a ", Int32),       // 2
+        (" aa.iiii       a ", Int64),       // 3
+        (" aaa.ii        a ", Decimal),     // 4
+        (" aaaa.i        a ", Float32),     // 5
+        (" aaaaa.        a ", Float64),     // 6
+        ("      e.       a ", Int256),      // 7
+        ("        .ii    a ", Date),        // 8
+        ("        a.ia   a ", Timestamp),   // 9
+        ("        aa.a   a ", Timestamptz), // A
+        ("           .i  a ", Time),        // B
+        ("           a.  a ", Interval),    // C
+        ("eeeeeee      . a ", Jsonb),       // D
+        ("              .a ", Bytea),       // E
+        ("eeeeeeeeeeeeeee. ", Varchar),     // F
+        ("   e            .", Serial),
     ];
     let mut map = BTreeMap::new();
     for (row, source) in CAST_TABLE {