diff --git a/internal/mcp/server.go b/internal/mcp/server.go
index c6bc599..240b437 100644
--- a/internal/mcp/server.go
+++ b/internal/mcp/server.go
@@ -158,13 +158,24 @@ func NewServer(opts Options) (*Server, error) {
 		al = &auditLogger{} // no-op: enc is nil, log() returns early
 	}
 
+	// Resolve the profile once for both consumers (step-up + signer).
+	// SigningProfile is the explicit opt-in; empty means "use the active
+	// profile." Pre-KLA-420 this fallback lived only in the signer block,
+	// so a webhook-only setup (no signing) emitted `"profile": ""` in
+	// every outbound envelope. Receivers keying on profile (Slack bot
+	// routing rules, audit dashboards) saw empty strings.
+	profile := opts.SigningProfile
+	if profile == "" {
+		profile = config.ActiveProfile()
+	}
+
 	stepUp := opts.stepUp
 	if stepUp == nil {
 		su, err := newStepUp(stepUpConfig{
 			Required:            opts.RequireStepUp,
 			APIKey:              opts.StepUpAPIKey,
 			AuthenticatorPref:   opts.StepUpAuthenticator,
-			Profile:             opts.SigningProfile,
+			Profile:             profile,
 			WebhookURL:          opts.ApprovalWebhookURL,
 			WebhookCallbackAddr: opts.ApprovalCallbackAddr,
 			WebhookTimeout:      opts.ApprovalTimeout,
@@ -177,10 +188,6 @@ func NewServer(opts Options) (*Server, error) {
 
 	signer := opts.signer
 	if signer == nil {
-		profile := opts.SigningProfile
-		if profile == "" {
-			profile = config.ActiveProfile()
-		}
 		signer = newSigner(opts.SignDestructiveOps, profile)
 	}
 
diff --git a/internal/mcp/stepup_webhook_test.go b/internal/mcp/stepup_webhook_test.go
index 7ac86bb..3559557 100644
--- a/internal/mcp/stepup_webhook_test.go
+++ b/internal/mcp/stepup_webhook_test.go
@@ -125,6 +125,62 @@ func TestWebhookStepUp_RemediationIsChannelAware(t *testing.T) {
 	}
 }
 
+// KLA-420: when an operator enables --require-step-up
+// --step-up-authenticator=webhook without also enabling signing
+// (mcp.sign_destructive_ops), the webhook envelope's profile field
+// must still carry the active profile name. Pre-fix, server.go wired
+// Profile = opts.SigningProfile directly with no fallback, so
+// webhook-only setups emitted `"profile": ""` to receivers.
+func TestNewServer_WebhookProfileFallsBackToActiveProfile(t *testing.T) {
+	setupTest(t)
+
+	s := MustNewServer(Options{
+		RequireStepUp:        true,
+		StepUpAuthenticator:  "webhook",
+		ApprovalWebhookURL:   "http://127.0.0.1:1/notused",
+		ApprovalCallbackAddr: "127.0.0.1:0",
+		ApprovalTimeout:      1 * time.Second,
+		// SigningProfile intentionally left empty — that's the bug:
+		// pre-fix this would propagate `profile: ""` into the webhook.
+	})
+	t.Cleanup(s.shutdownStepUp)
+
+	w, ok := s.stepUp.(*webhookStepUp)
+	if !ok {
+		t.Fatalf("expected *webhookStepUp, got %T", s.stepUp)
+	}
+	// setupTest configures active_profile=default; resolution must pick
+	// that up rather than leaving the field empty.
+	if w.profile != "default" {
+		t.Errorf("webhookStepUp.profile = %q, want %q (active profile fallback)", w.profile, "default")
+	}
+}
+
+// Companion: an explicit SigningProfile must still flow through
+// unchanged. The fallback only kicks in when the explicit value is
+// empty.
+func TestNewServer_WebhookProfileHonorsExplicitSigningProfile(t *testing.T) {
+	setupTest(t)
+
+	s := MustNewServer(Options{
+		RequireStepUp:        true,
+		StepUpAuthenticator:  "webhook",
+		ApprovalWebhookURL:   "http://127.0.0.1:1/notused",
+		ApprovalCallbackAddr: "127.0.0.1:0",
+		ApprovalTimeout:      1 * time.Second,
+		SigningProfile:       "staging",
+	})
+	t.Cleanup(s.shutdownStepUp)
+
+	w, ok := s.stepUp.(*webhookStepUp)
+	if !ok {
+		t.Fatalf("expected *webhookStepUp, got %T", s.stepUp)
+	}
+	if w.profile != "staging" {
+		t.Errorf("webhookStepUp.profile = %q, want %q (explicit SigningProfile)", w.profile, "staging")
+	}
+}
+
 func TestNewWebhookStepUp_RejectsEmptyURL(t *testing.T) {
 	_, err := newWebhookStepUp("", "", 0, "default")
 	if err == nil {