diff --git a/common/configuration/manager_test.go b/common/configuration/manager_test.go
index 56c620ad5f..042391af3c 100644
--- a/common/configuration/manager_test.go
+++ b/common/configuration/manager_test.go
@@ -8,6 +8,7 @@ import (
 	"testing"
 
 	"github.com/alecthomas/assert/v2"
+	"github.com/alecthomas/types/optional"
 	"github.com/zalando/go-keyring"
 
 	"github.com/TBD54566975/ftl/internal/log"
@@ -54,6 +55,7 @@ func TestManager(t *testing.T) {
 			{Ref: Ref{Name: "baz"}, Accessor: URL("envar://baz")},
 			{Ref: Ref{Name: "foo"}, Accessor: URL("inline://ImJhciI")},
 			{Ref: Ref{Name: "mutable"}, Accessor: URL("inline://ImhlbGxvIg")},
+			{Ref: Ref{Module: optional.Some[string]("echo"), Name: "default"}, Accessor: URL("inline://ImFub255bW91cyI")},
 		})
 	})
 }
diff --git a/common/configuration/projectconfig_resolver.go b/common/configuration/projectconfig_resolver.go
index dbfe23dd97..5becd68eef 100644
--- a/common/configuration/projectconfig_resolver.go
+++ b/common/configuration/projectconfig_resolver.go
@@ -101,9 +101,9 @@ func (p ProjectConfigResolver[R]) getMapping(config pc.Config, module optional.O
 	get := func(dest pc.ConfigAndSecrets) map[string]*pc.URL {
 		switch any(k).(type) {
 		case Configuration:
-			return dest.Config
+			return emptyMapIfNil(dest.Config)
 		case Secrets:
-			return dest.Secrets
+			return emptyMapIfNil(dest.Secrets)
 		default:
 			panic("unsupported kind")
 		}
@@ -121,6 +121,13 @@ func (p ProjectConfigResolver[R]) getMapping(config pc.Config, module optional.O
 	return mapping, nil
 }
 
+func emptyMapIfNil(mapping map[string]*pc.URL) map[string]*pc.URL {
+	if mapping == nil {
+		return map[string]*pc.URL{}
+	}
+	return mapping
+}
+
 func (p ProjectConfigResolver[R]) setMapping(config pc.Config, module optional.Option[string], mapping map[string]*pc.URL) error {
 	var k R
 	set := func(dest *pc.ConfigAndSecrets, mapping map[string]*pc.URL) {
@@ -143,5 +150,8 @@ func (p ProjectConfigResolver[R]) setMapping(config pc.Config, module optional.O
 		set(&config.Global, mapping)
 	}
 	configPaths := pc.ConfigPaths(p.Config)
+	if len(configPaths) == 0 {
+		return pc.Save(pc.GetDefaultConfigPath(), config)
+	}
 	return pc.Save(configPaths[len(configPaths)-1], config)
 }
diff --git a/common/configuration/projectconfig_resolver_test.go b/common/configuration/projectconfig_resolver_test.go
new file mode 100644
index 0000000000..ceda91717b
--- /dev/null
+++ b/common/configuration/projectconfig_resolver_test.go
@@ -0,0 +1,63 @@
+package configuration
+
+import (
+	"context"
+	"net/url"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/alecthomas/assert/v2"
+	"github.com/alecthomas/types/optional"
+
+	"github.com/TBD54566975/ftl/common/projectconfig"
+	"github.com/TBD54566975/ftl/internal/log"
+)
+
+func TestSet(t *testing.T) {
+	defaultPath := projectconfig.GetDefaultConfigPath()
+	origConfigBytes, err := os.ReadFile(defaultPath)
+	assert.NoError(t, err)
+
+	config := filepath.Join(t.TempDir(), "ftl-project.toml")
+	existing, err := os.ReadFile("testdata/ftl-project.toml")
+	assert.NoError(t, err)
+	err = os.WriteFile(config, existing, 0600)
+	assert.NoError(t, err)
+
+	t.Run("ExistingModule", func(t *testing.T) {
+		setAndAssert(t, "echo", []string{config})
+	})
+	t.Run("NewModule", func(t *testing.T) {
+		setAndAssert(t, "echooo", []string{config})
+	})
+	t.Run("MissingTOMLFile", func(t *testing.T) {
+		err := os.Remove(config)
+		assert.NoError(t, err)
+		setAndAssert(t, "echooooo", []string{})
+		err = os.WriteFile(defaultPath, origConfigBytes, 0600)
+		assert.NoError(t, err)
+	})
+}
+
+func setAndAssert(t *testing.T, module string, config []string) {
+	t.Helper()
+
+	ctx := log.ContextWithNewDefaultLogger(context.Background())
+
+	cf, err := New(ctx,
+		ProjectConfigResolver[Configuration]{Config: config},
+		[]Provider[Configuration]{
+			EnvarProvider[Configuration]{},
+			InlineProvider[Configuration]{Inline: true}, // Writer
+		})
+	assert.NoError(t, err)
+
+	var got *url.URL
+	want := URL("inline://asdfasdf")
+	err = cf.Set(ctx, Ref{Module: optional.Some[string](module), Name: "default"}, want)
+	assert.NoError(t, err)
+	err = cf.Get(ctx, Ref{Module: optional.Some[string](module), Name: "default"}, &got)
+	assert.NoError(t, err)
+	assert.Equal(t, want, got)
+}
diff --git a/common/configuration/testdata/ftl-project.toml b/common/configuration/testdata/ftl-project.toml
index 94a29f2ba9..962394b673 100644
--- a/common/configuration/testdata/ftl-project.toml
+++ b/common/configuration/testdata/ftl-project.toml
@@ -8,3 +8,8 @@ mutable = "keychain://mutable"
 baz = "envar://baz"
 foo = "inline://ImJhciI"
 mutable = "inline://ImhlbGxvIg"
+
+[modules]
+  [modules.echo]
+    [modules.echo.configuration]
+      default = "inline://ImFub255bW91cyI"
diff --git a/common/projectconfig/projectconfig.go b/common/projectconfig/projectconfig.go
index 207e324d66..4711bb3d4b 100644
--- a/common/projectconfig/projectconfig.go
+++ b/common/projectconfig/projectconfig.go
@@ -42,7 +42,7 @@ func ConfigPaths(input []string) []string {
 	if len(input) > 0 {
 		return input
 	}
-	path := filepath.Join(internal.GitRoot(""), "ftl-project.toml")
+	path := GetDefaultConfigPath()
 	_, err := os.Stat(path)
 	if err == nil {
 		return []string{path}
@@ -50,6 +50,10 @@ func ConfigPaths(input []string) []string {
 	return []string{}
 }
 
+func GetDefaultConfigPath() string {
+	return filepath.Join(internal.GitRoot(""), "ftl-project.toml")
+}
+
 func LoadConfig(ctx context.Context, input []string) (Config, error) {
 	logger := log.FromContext(ctx)
 	configPaths := ConfigPaths(input)