diff --git a/introspection-engine/introspection-engine-tests/tests/named_constraints/mod.rs b/introspection-engine/introspection-engine-tests/tests/named_constraints/mod.rs
index 283139a189d7..6f9f6b6fc7e4 100644
--- a/introspection-engine/introspection-engine-tests/tests/named_constraints/mod.rs
+++ b/introspection-engine/introspection-engine-tests/tests/named_constraints/mod.rs
@@ -5,6 +5,7 @@ use introspection_engine_tests::test_api::TestApi;
 use introspection_engine_tests::test_api::*;
 
 use introspection_engine_tests::TestResult;
+use quaint::prelude::Queryable;
 use test_macros::test_connector;
 
 #[test_connector(preview_features("NamedConstraints"), tags(Mssql, Postgres))]
@@ -359,3 +360,45 @@ async fn introspecting_custom_fk_names_does_not_return_them_on_sqlite(api: &Test
 
     Ok(())
 }
+
+#[test_connector(preview_features("NamedConstraints"), tags(Mssql))]
+async fn introspecting_custom_default_names_should_output_to_dml(api: &TestApi) -> TestResult {
+    let create_table = format!(
+        "CREATE TABLE [{}].[custom_defaults_test] (id INT CONSTRAINT pk_meow PRIMARY KEY, data NVARCHAR(255) CONSTRAINT meow DEFAULT 'foo')",
+        api.schema_name()
+    );
+
+    api.database().raw_cmd(&create_table).await?;
+
+    let dm = r#"
+        model custom_defaults_test {
+            id   Int     @id(map: "pk_meow")
+            data String? @default("foo", map: "meow") @db.NVarChar(255)
+        }
+    "#;
+
+    api.assert_eq_datamodels(&dm, &api.introspect().await?);
+
+    Ok(())
+}
+
+#[test_connector(preview_features("NamedConstraints"), tags(Mssql))]
+async fn introspecting_default_default_names_should_not_output_to_dml(api: &TestApi) -> TestResult {
+    let create_table = format!(
+        "CREATE TABLE [{}].[custom_defaults_test] (id INT CONSTRAINT pk_meow PRIMARY KEY, data NVARCHAR(255) CONSTRAINT custom_defaults_test_data_df DEFAULT 'foo')",
+        api.schema_name()
+    );
+
+    api.database().raw_cmd(&create_table).await?;
+
+    let dm = indoc! {r#"
+        model custom_defaults_test {
+          id   Int     @id(map: "pk_meow")
+          data String? @default("foo") @db.NVarChar(255)
+        }
+    "#};
+
+    api.assert_eq_datamodels(&dm, &api.introspect().await?);
+
+    Ok(())
+}
diff --git a/libs/datamodel/connectors/dml/src/default_value.rs b/libs/datamodel/connectors/dml/src/default_value.rs
index 7cf64b4649e8..b1b0a02efe8f 100644
--- a/libs/datamodel/connectors/dml/src/default_value.rs
+++ b/libs/datamodel/connectors/dml/src/default_value.rs
@@ -117,6 +117,11 @@ impl DefaultValue {
             _ => None,
         }
     }
+
+    /// The default value constraint name.
+    pub fn db_name(&self) -> Option<&str> {
+        self.db_name.as_ref().map(|s| s.as_str())
+    }
 }
 
 #[derive(Clone)]
diff --git a/libs/datamodel/connectors/dml/src/field.rs b/libs/datamodel/connectors/dml/src/field.rs
index aff48f4a9727..2a599fc8eefd 100644
--- a/libs/datamodel/connectors/dml/src/field.rs
+++ b/libs/datamodel/connectors/dml/src/field.rs
@@ -431,6 +431,7 @@ impl ScalarField {
             is_ignored: false,
         }
     }
+
     /// Creates a new field with the given name and type, marked as generated and optional.
     pub fn new_generated(name: &str, field_type: FieldType) -> ScalarField {
         let mut field = Self::new(name, FieldArity::Optional, field_type);
@@ -461,9 +462,13 @@ impl ScalarField {
     }
 
     pub fn is_auto_increment(&self) -> bool {
-        let kind = self.default_value.as_ref().map(|val| &val.kind);
+        let kind = self.default_value().map(|val| &val.kind);
         matches!(kind, Some(DefaultKind::Expression(ref expr)) if expr == &ValueGenerator::new_autoincrement())
     }
+
+    pub fn default_value(&self) -> Option<&DefaultValue> {
+        self.default_value.as_ref()
+    }
 }
 
 impl WithName for ScalarField {
diff --git a/libs/datamodel/core/src/ast/attribute.rs b/libs/datamodel/core/src/ast/attribute.rs
index bee520c5f777..bc9b34f421d2 100644
--- a/libs/datamodel/core/src/ast/attribute.rs
+++ b/libs/datamodel/core/src/ast/attribute.rs
@@ -23,6 +23,10 @@ impl Attribute {
     pub fn is_index(&self) -> bool {
         matches!(self.name.name.as_str(), "index" | "unique")
     }
+
+    pub fn is_id(&self) -> bool {
+        matches!(self.name.name.as_str(), "id")
+    }
 }
 
 impl WithIdentifier for Attribute {
diff --git a/libs/datamodel/core/src/ast/model.rs b/libs/datamodel/core/src/ast/model.rs
index 01e41f1974b1..cffac0f9d9c0 100644
--- a/libs/datamodel/core/src/ast/model.rs
+++ b/libs/datamodel/core/src/ast/model.rs
@@ -52,6 +52,16 @@ impl Model {
     pub(crate) fn find_field_bang(&self, name: &str) -> &Field {
         self.find_field(name).unwrap()
     }
+
+    pub(crate) fn id_attribute(&self) -> &Attribute {
+        let from_model = self.attributes().iter().find(|attr| attr.is_id());
+
+        let mut from_field = self
+            .iter_fields()
+            .flat_map(|(_, field)| field.attributes().iter().find(|attr| attr.is_id()));
+
+        from_model.or_else(|| from_field.next()).unwrap()
+    }
 }
 
 impl WithIdentifier for Model {
diff --git a/libs/datamodel/core/src/transform/ast_to_dml/validate.rs b/libs/datamodel/core/src/transform/ast_to_dml/validate.rs
index 9a9026223fa0..d976fecc3d94 100644
--- a/libs/datamodel/core/src/transform/ast_to_dml/validate.rs
+++ b/libs/datamodel/core/src/transform/ast_to_dml/validate.rs
@@ -1,16 +1,19 @@
 #![allow(clippy::suspicious_operation_groupings)] // clippy is wrong there
-use crate::common::constraint_names::ConstraintNames;
-use crate::PreviewFeature::NamedConstraints;
+
+mod names;
+
 use crate::{
     ast::{self, Span},
-    common::preview_features::PreviewFeature,
+    common::{constraint_names::ConstraintNames, preview_features::PreviewFeature},
     configuration,
     diagnostics::{DatamodelError, Diagnostics},
     dml,
+    PreviewFeature::NamedConstraints,
 };
 use ::dml::{datamodel::Datamodel, field::RelationField, model::Model, traits::WithName};
 use datamodel_connector::ConnectorCapability;
 use enumflags2::BitFlags;
+use names::NamesValidator;
 use std::collections::HashSet;
 
 /// Helper for validating a datamodel.
@@ -39,7 +42,7 @@ impl<'a> Validator<'a> {
         }
     }
 
-    pub(crate) fn validate(&self, ast: &ast::SchemaAst, schema: &mut dml::Datamodel, diagnostics: &mut Diagnostics) {
+    pub(crate) fn validate(&self, ast: &ast::SchemaAst, schema: &dml::Datamodel, diagnostics: &mut Diagnostics) {
         for model in schema.models() {
             let ast_model = ast.find_model(&model.name).expect(STATE_ERROR);
 
@@ -107,17 +110,51 @@ impl<'a> Validator<'a> {
         }
     }
 
-    pub fn post_standardisation_validate(
+    pub(crate) fn post_standardisation_validate(
         &self,
         ast_schema: &ast::SchemaAst,
-        schema: &mut dml::Datamodel,
+        schema: &dml::Datamodel,
         diagnostics: &mut Diagnostics,
     ) {
+        let constraint_names = NamesValidator::new(&schema, self.preview_features, self.source);
+
         for model in schema.models() {
+            let ast_model = ast_schema.find_model(&model.name).expect(STATE_ERROR);
+
+            if let Some(pk) = &model.primary_key {
+                if let Some(name) = &pk.db_name {
+                    // Only for SQL Server for now...
+                    if constraint_names.is_duplicate(name) {
+                        let span = ast_model.id_attribute().span;
+                        let message = "Given constraint name is already in use in the data model.";
+                        let error = DatamodelError::new_attribute_validation_error(message, "default", span);
+
+                        diagnostics.push_error(error);
+                    }
+                }
+            }
+
+            // TODO: Extend this check for other constraints. Now only used
+            // for SQL Server default constraint names.
+            for field in model.fields().filter(|f| f.is_scalar_field()) {
+                if let Some(name) = field.default_value().and_then(|d| d.db_name()) {
+                    let ast_field = ast_model.find_field_bang(field.name());
+
+                    if constraint_names.is_duplicate(name) {
+                        let message = "Given constraint name is already in use in the data model.";
+                        let span = ast_field.span_for_argument("default", "map");
+                        let error = DatamodelError::new_attribute_validation_error(message, "default", span);
+
+                        diagnostics.push_error(error);
+                    }
+                }
+            }
+
             let mut new_errors = self.validate_relation_arguments_bla(
                 schema,
                 ast_schema.find_model(&model.name).expect(STATE_ERROR),
                 model,
+                &constraint_names,
             );
 
             diagnostics.append(&mut new_errors);
@@ -544,11 +581,12 @@ impl<'a> Validator<'a> {
         }
     }
 
-    fn validate_relation_arguments_bla(
+    fn validate_relation_arguments_bla<'dml>(
         &self,
-        datamodel: &dml::Datamodel,
+        datamodel: &'dml dml::Datamodel,
         ast_model: &ast::Model,
         model: &dml::Model,
+        constraint_names: &NamesValidator<'dml>,
     ) -> Diagnostics {
         let mut errors = Diagnostics::new();
 
@@ -563,6 +601,20 @@ impl<'a> Validator<'a> {
             let rel_info = &field.relation_info;
             let related_model = datamodel.find_model(&rel_info.to).expect(STATE_ERROR);
 
+            if let Some(name) = field.relation_info.fk_name.as_ref() {
+                // Only for SQL Server for now...
+                if constraint_names.is_duplicate(name) {
+                    let span = ast_field
+                        .map(|f| f.span_for_argument("relation", "map"))
+                        .unwrap_or_else(ast::Span::empty);
+
+                    let message = "Given constraint name is already in use in the data model.";
+                    let error = DatamodelError::new_attribute_validation_error(message, RELATION_ATTRIBUTE_NAME, span);
+
+                    errors.push_error(error);
+                }
+            }
+
             if let Some((_rel_field_idx, related_field)) = datamodel.find_related_field(field) {
                 let related_field_rel_info = &related_field.relation_info;
 
diff --git a/libs/datamodel/core/src/transform/ast_to_dml/validation_pipeline.rs b/libs/datamodel/core/src/transform/ast_to_dml/validation_pipeline.rs
index edb9794cb4c3..1a961d9acaad 100644
--- a/libs/datamodel/core/src/transform/ast_to_dml/validation_pipeline.rs
+++ b/libs/datamodel/core/src/transform/ast_to_dml/validation_pipeline.rs
@@ -80,7 +80,7 @@ impl<'a, 'b> ValidationPipeline<'a> {
 
         // Phase 6: Post Standardisation Validation
         self.validator
-            .post_standardisation_validate(ast_schema, &mut schema, &mut diagnostics);
+            .post_standardisation_validate(ast_schema, &schema, &mut diagnostics);
 
         diagnostics.to_result()?;
 
diff --git a/libs/datamodel/core/src/transform/dml_to_ast/lower_field.rs b/libs/datamodel/core/src/transform/dml_to_ast/lower_field.rs
index cb08211ca007..d8643ceb2f58 100644
--- a/libs/datamodel/core/src/transform/dml_to_ast/lower_field.rs
+++ b/libs/datamodel/core/src/transform/dml_to_ast/lower_field.rs
@@ -7,6 +7,8 @@ use crate::{
     ast::{self, Attribute, Span},
     dml, Datasource, Field, Ignorable,
 };
+use ::dml::traits::WithName;
+use datamodel_connector::{Connector, EmptyDatamodelConnector};
 use prisma_value::PrismaValue;
 
 impl<'a> LowerDmlToAst<'a> {
@@ -109,13 +111,27 @@ impl<'a> LowerDmlToAst<'a> {
 
         // @default
         if let Some(default_value) = field.default_value() {
-            attributes.push(ast::Attribute::new(
-                "default",
-                vec![ast::Argument::new(
-                    "",
-                    LowerDmlToAst::<'a>::lower_default_value(default_value.clone()),
-                )],
-            ));
+            let mut args = vec![ast::Argument::new(
+                "",
+                LowerDmlToAst::<'a>::lower_default_value(default_value.clone()),
+            )];
+
+            if self.preview_features.contains(PreviewFeature::NamedConstraints) {
+                let connector = self
+                    .datasource
+                    .map(|source| source.active_connector.as_ref())
+                    .unwrap_or(&EmptyDatamodelConnector as &dyn Connector);
+
+                let prisma_default = ConstraintNames::default_name(model.name(), field.name(), connector);
+
+                if let Some(name) = default_value.db_name() {
+                    if name != &prisma_default {
+                        args.push(ast::Argument::new("map", Self::lower_string(name)))
+                    }
+                }
+            }
+
+            attributes.push(ast::Attribute::new("default", args));
         }
 
         // @updatedAt
@@ -224,19 +240,23 @@ impl<'a> LowerDmlToAst<'a> {
         }
     }
 
+    pub fn lower_string(s: impl ToString) -> ast::Expression {
+        ast::Expression::StringValue(s.to_string(), ast::Span::empty())
+    }
+
     pub fn lower_prisma_value(pv: &PrismaValue) -> ast::Expression {
         match pv {
             PrismaValue::Boolean(true) => ast::Expression::BooleanValue(String::from("true"), ast::Span::empty()),
             PrismaValue::Boolean(false) => ast::Expression::BooleanValue(String::from("false"), ast::Span::empty()),
-            PrismaValue::String(value) => ast::Expression::StringValue(value.clone(), ast::Span::empty()),
+            PrismaValue::String(value) => Self::lower_string(value),
             PrismaValue::Enum(value) => ast::Expression::ConstantValue(value.clone(), ast::Span::empty()),
-            PrismaValue::DateTime(value) => ast::Expression::StringValue(value.to_rfc3339(), ast::Span::empty()),
+            PrismaValue::DateTime(value) => Self::lower_string(value),
             PrismaValue::Float(value) => ast::Expression::NumericValue(value.to_string(), ast::Span::empty()),
             PrismaValue::Int(value) => ast::Expression::NumericValue(value.to_string(), ast::Span::empty()),
             PrismaValue::BigInt(value) => ast::Expression::NumericValue(value.to_string(), ast::Span::empty()),
             PrismaValue::Null => ast::Expression::ConstantValue("null".to_string(), ast::Span::empty()),
-            PrismaValue::Uuid(val) => ast::Expression::StringValue(val.to_string(), ast::Span::empty()),
-            PrismaValue::Json(val) => ast::Expression::StringValue(val.to_string(), ast::Span::empty()),
+            PrismaValue::Uuid(val) => Self::lower_string(val),
+            PrismaValue::Json(val) => Self::lower_string(val),
             PrismaValue::List(vec) => ast::Expression::Array(
                 vec.iter()
                     .map(|pv| LowerDmlToAst::<'a>::lower_prisma_value(pv))
diff --git a/libs/datamodel/core/tests/attributes/default_negative.rs b/libs/datamodel/core/tests/attributes/default_negative.rs
index 4fda8ce11830..e9ffab44c7cc 100644
--- a/libs/datamodel/core/tests/attributes/default_negative.rs
+++ b/libs/datamodel/core/tests/attributes/default_negative.rs
@@ -427,7 +427,18 @@ fn named_default_constraints_cannot_have_duplicate_names() {
     let error = datamodel::parse_schema(dml).map(drop).unwrap_err();
 
     let expectation = expect![[r#"
-        TODO: Talk with Matthias on Monday!
+        error: Error parsing attribute "@default": Given constraint name is already in use in the data model.
+          -->  schema.prisma:13
+           | 
+        12 |     id Int @id @default(autoincrement())
+        13 |     a  String @default("asdf", map: "reserved")
+           | 
+        error: Error parsing attribute "@default": Given constraint name is already in use in the data model.
+          -->  schema.prisma:18
+           | 
+        17 |     id Int @id @default(autoincrement())
+        18 |     b  String @default("asdf", map: "reserved")
+           | 
     "#]];
 
     expectation.assert_eq(&error)
@@ -459,7 +470,18 @@ fn named_default_constraints_cannot_clash_with_pk_names() {
     let error = datamodel::parse_schema(dml).map(drop).unwrap_err();
 
     let expectation = expect![[r#"
-        TODO: Talk with Matthias on Monday!
+        error: Error parsing attribute "@default": Given constraint name is already in use in the data model.
+          -->  schema.prisma:13
+           | 
+        12 |     id Int @id @default(autoincrement())
+        13 |     a  String @default("asdf", map: "reserved")
+           | 
+        error: Error parsing attribute "@default": Given constraint name is already in use in the data model.
+          -->  schema.prisma:17
+           | 
+        16 | model B {
+        17 |     id Int @id(map: "reserved") @default(autoincrement())
+           | 
     "#]];
 
     expectation.assert_eq(&error)
@@ -480,13 +502,13 @@ fn named_default_constraints_cannot_clash_with_fk_names() {
 
         model A {
             id  Int @id @default(autoincrement())
-            a   String @default("asdf", map: "reserved")
-            b   B      @relation(fields: [bId], references: [id], map: "name")
+            a   String  @default("asdf", map: "reserved")
+            b   B       @relation(fields: [bId], references: [id], map: "reserved")
             bId Int
         }
 
         model B {
-            id Int @id(map: "reserved") @default(autoincrement())
+            id Int @id @default(autoincrement())
             as A[]
         }
     "#};
@@ -494,7 +516,18 @@ fn named_default_constraints_cannot_clash_with_fk_names() {
     let error = datamodel::parse_schema(dml).map(drop).unwrap_err();
 
     let expectation = expect![[r#"
-        TODO: Talk with Matthias on Monday!
+        error: Error parsing attribute "@default": Given constraint name is already in use in the data model.
+          -->  schema.prisma:13
+           | 
+        12 |     id  Int @id @default(autoincrement())
+        13 |     a   String  @default("asdf", map: "reserved")
+           | 
+        error: Error parsing attribute "@relation": Given constraint name is already in use in the data model.
+          -->  schema.prisma:14
+           | 
+        13 |     a   String  @default("asdf", map: "reserved")
+        14 |     b   B       @relation(fields: [bId], references: [id], map: "reserved")
+           | 
     "#]];
 
     expectation.assert_eq(&error)
diff --git a/libs/datamodel/core/tests/attributes/default_positive.rs b/libs/datamodel/core/tests/attributes/default_positive.rs
index 4abed0785a2d..e60b92aded9b 100644
--- a/libs/datamodel/core/tests/attributes/default_positive.rs
+++ b/libs/datamodel/core/tests/attributes/default_positive.rs
@@ -149,3 +149,94 @@ fn named_default_constraints_should_work_on_sql_server() {
         .assert_has_scalar_field("data")
         .assert_default_value(expected_default);
 }
+
+// TODO: Change me when we do validate
+#[test]
+fn named_default_constraints_should_not_validate_name_clashes_on_pk() {
+    let dml = indoc! { r#"
+        datasource test {
+            provider = "postgres"
+            url = "postgres://"
+        }
+
+        generator js {
+            provider = "prisma-client-js"
+            previewFeatures = ["namedConstraints"]
+        }
+
+        model A {
+            id Int @id(map: "meow") @default(autoincrement())
+        }
+
+        model B {
+            id Int @id(map: "meow") @default(autoincrement())
+        }
+    "#};
+
+    assert!(datamodel::parse_schema(dml).is_ok());
+}
+
+// TODO: Change me when we do validate
+#[test]
+fn named_default_constraints_should_not_validate_name_clashes_on_pk_fk() {
+    let dml = indoc! { r#"
+        datasource test {
+            provider = "postgres"
+            url = "postgres://"
+        }
+
+        generator js {
+            provider = "prisma-client-js"
+            previewFeatures = ["namedConstraints"]
+        }
+
+        model A {
+            id  Int @id(map: "meow") @default(autoincrement())
+            b   B   @relation(fields: [bId], references: [id], map: "meow")
+            bId Int
+        }
+
+        model B {
+            id Int @id(map: "meow") @default(autoincrement())
+            as A[]
+        }
+    "#};
+
+    assert!(datamodel::parse_schema(dml).is_ok());
+}
+
+// TODO: Change me when we do validate
+#[test]
+fn named_default_constraints_should_not_validate_name_clashes_on_fk() {
+    let dml = indoc! { r#"
+        datasource test {
+            provider = "postgres"
+            url = "postgres://"
+        }
+
+        generator js {
+            provider = "prisma-client-js"
+            previewFeatures = ["namedConstraints"]
+        }
+
+        model A {
+            id  Int @id(map: "meow") @default(autoincrement())
+            b   B   @relation(fields: [bId], references: [id], map: "meow")
+            c   C   @relation(fields: [cId], references: [id], map: "meow")
+            bId Int
+            cId Int
+        }
+
+        model B {
+            id Int @id @default(autoincrement())
+            as A[]
+        }
+
+        model C {
+            id Int @id @default(autoincrement())
+            as A[]
+        }
+    "#};
+
+    assert!(datamodel::parse_schema(dml).is_ok());
+}
diff --git a/migration-engine/migration-engine-tests/tests/migrations/defaults.rs b/migration-engine/migration-engine-tests/tests/migrations/defaults.rs
index 748f6ce84653..8a57b9720a7c 100644
--- a/migration-engine/migration-engine-tests/tests/migrations/defaults.rs
+++ b/migration-engine/migration-engine-tests/tests/migrations/defaults.rs
@@ -215,6 +215,32 @@ fn column_defaults_must_be_migrated(api: TestApi) {
     });
 }
 
+#[test_connector(tags(Mssql))]
+fn default_constraint_names_should_work(api: TestApi) {
+    let dm = r#"
+        generator js {
+            provider = "prisma-client-js"
+            previewFeatures = ["microsoftSqlServer", "namedConstraints"]
+        }
+
+        model A {
+            id Int @id @default(autoincrement())
+            data String @default("beeb buub", map: "meow")
+        }
+    "#;
+
+    api.schema_push_w_datasource(dm).send().assert_green_bang();
+
+    api.assert_schema().assert_table("A", |table| {
+        table.assert_column("data", |col| {
+            let mut expected = DefaultValue::value("beeb buub");
+            expected.set_constraint_name("meow");
+
+            col.assert_default(Some(expected))
+        })
+    });
+}
+
 #[test_connector]
 fn escaped_string_defaults_are_not_arbitrarily_migrated(api: TestApi) {
     use quaint::ast::Insert;