diff --git a/common/build.rs b/common/build.rs
index 323746b..1d71c08 100644
--- a/common/build.rs
+++ b/common/build.rs
@@ -169,10 +169,6 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
             ".komp_ac.table_definition.AddTableColumnsRequest",
             "#[derive(serde::Serialize, serde::Deserialize)]",
         )
-        .type_attribute(
-            ".komp_ac.table_definition.MoneyColumnOptions",
-            "#[derive(serde::Serialize, serde::Deserialize)]",
-        )
         .type_attribute(
             ".komp_ac.table_definition.TableDefinitionResponse",
             "#[derive(serde::Serialize, serde::Deserialize)]"
diff --git a/common/proto/table_definition.proto b/common/proto/table_definition.proto
index fd0110a..6ebc2ea 100644
--- a/common/proto/table_definition.proto
+++ b/common/proto/table_definition.proto
@@ -78,9 +78,8 @@ message PostTableDefinitionRequest {
   // like "public", "information_schema", or ones starting with "pg_".
   string profile_name = 5;
 
+  // ISO-4217 base currency used by every MONEY column in this table.
   string base_currency = 6;
-  repeated MoneyColumnOptions money_columns = 7;
-
 }
 
 // Defines append-only column additions for an existing table.
@@ -97,8 +96,8 @@ message AddTableColumnsRequest {
   // Optional indexes for the new columns only.
   repeated string indexes = 4;
 
-  repeated MoneyColumnOptions money_columns = 5;
-  string base_currency = 6;
+  // Required when adding the first MONEY column to a table.
+  string base_currency = 5;
 
 }
 
@@ -107,12 +106,6 @@ enum MoneyRounding {
   MONEY_ROUNDING_HALF_UP = 1;
 }
 
-message MoneyColumnOptions {
-  string column_name = 1;
-  bool immutable = 2;
-  MoneyRounding rounding = 3;
-}
-
 // Describes one user-defined column for a table.
 message ColumnDefinition {
   // Column name that follows the same validation rules as table_name.
@@ -132,6 +125,12 @@ message ColumnDefinition {
   // DECIMAL args must be integers (no sign, no dot, no leading zeros);
   // s ≤ p and p ≥ 1.
   string field_type = 2;
+
+  // Once initially stored, this column can never be changed.
+  bool immutable = 3;
+
+  // MONEY rounding applied before an immutable value is initially stored.
+  MoneyRounding rounding = 4;
 }
 
 // Response after table creation (success + DDL preview).
@@ -229,7 +228,6 @@ message TableDetail {
   repeated ColumnDefinition columns = 3;
   repeated ScriptInfo scripts = 4;
   string base_currency = 5;
-  repeated MoneyColumnOptions money_columns = 6;
 }
 
 // A script that targets a specific column in a table.
diff --git a/common/src/proto/descriptor.bin b/common/src/proto/descriptor.bin
index c1e613a..f13befb 100644
Binary files a/common/src/proto/descriptor.bin and b/common/src/proto/descriptor.bin differ
diff --git a/common/src/proto/komp_ac.table_definition.rs b/common/src/proto/komp_ac.table_definition.rs
index c7de2fa..705a952 100644
--- a/common/src/proto/komp_ac.table_definition.rs
+++ b/common/src/proto/komp_ac.table_definition.rs
@@ -42,10 +42,9 @@ pub struct PostTableDefinitionRequest {
     /// like "public", "information_schema", or ones starting with "pg\_".
     #[prost(string, tag = "5")]
     pub profile_name: ::prost::alloc::string::String,
+    /// ISO-4217 base currency used by every MONEY column in this table.
     #[prost(string, tag = "6")]
     pub base_currency: ::prost::alloc::string::String,
-    #[prost(message, repeated, tag = "7")]
-    pub money_columns: ::prost::alloc::vec::Vec<MoneyColumnOptions>,
 }
 /// Defines append-only column additions for an existing table.
 #[derive(serde::Serialize, serde::Deserialize)]
@@ -63,21 +62,10 @@ pub struct AddTableColumnsRequest {
     /// Optional indexes for the new columns only.
     #[prost(string, repeated, tag = "4")]
     pub indexes: ::prost::alloc::vec::Vec<::prost::alloc::string::String>,
-    #[prost(message, repeated, tag = "5")]
-    pub money_columns: ::prost::alloc::vec::Vec<MoneyColumnOptions>,
-    #[prost(string, tag = "6")]
+    /// Required when adding the first MONEY column to a table.
+    #[prost(string, tag = "5")]
     pub base_currency: ::prost::alloc::string::String,
 }
-#[derive(serde::Serialize, serde::Deserialize)]
-#[derive(Clone, PartialEq, Eq, Hash, ::prost::Message)]
-pub struct MoneyColumnOptions {
-    #[prost(string, tag = "1")]
-    pub column_name: ::prost::alloc::string::String,
-    #[prost(bool, tag = "2")]
-    pub immutable: bool,
-    #[prost(enumeration = "MoneyRounding", tag = "3")]
-    pub rounding: i32,
-}
 /// Describes one user-defined column for a table.
 #[derive(serde::Serialize, serde::Deserialize)]
 #[derive(Clone, PartialEq, Eq, Hash, ::prost::Message)]
@@ -100,6 +88,12 @@ pub struct ColumnDefinition {
     /// s ≤ p and p ≥ 1.
     #[prost(string, tag = "2")]
     pub field_type: ::prost::alloc::string::String,
+    /// Once initially stored, this column can never be changed.
+    #[prost(bool, tag = "3")]
+    pub immutable: bool,
+    /// MONEY rounding applied before an immutable value is initially stored.
+    #[prost(enumeration = "MoneyRounding", tag = "4")]
+    pub rounding: i32,
 }
 /// Response after table creation (success + DDL preview).
 #[derive(serde::Serialize, serde::Deserialize)]
@@ -235,8 +229,6 @@ pub struct TableDetail {
     pub scripts: ::prost::alloc::vec::Vec<ScriptInfo>,
     #[prost(string, tag = "5")]
     pub base_currency: ::prost::alloc::string::String,
-    #[prost(message, repeated, tag = "6")]
-    pub money_columns: ::prost::alloc::vec::Vec<MoneyColumnOptions>,
 }
 /// A script that targets a specific column in a table.
 #[derive(Clone, PartialEq, Eq, Hash, ::prost::Message)]