diff --git a/checker/collect.go b/checker/collect.go
index 153ab32..7e1f4b5 100644
--- a/checker/collect.go
+++ b/checker/collect.go
@@ -21,6 +21,7 @@ import (
 	"time"
 
 	sdk "git.happydns.org/checker-sdk-go/checker"
+	happydns "git.happydns.org/happyDomain/model"
 	"golang.org/x/net/html"
 )
 
@@ -143,7 +144,22 @@ func buildTarget(ctx context.Context, opts sdk.CheckerOptions) (Target, error) {
 		userAgent = v
 	}
 
-	host, ips := addressesFromServer(server)
+	// Origin is the FQDN where the service is mounted: svc.Domain holds the
+	// subdomain (relative to apex; "@" for apex), and the domain_name
+	// autofill carries the zone apex.
+	apex := ""
+	if v, ok := sdk.GetOption[string](opts, OptionDomainName); ok {
+		apex = strings.TrimSuffix(v, ".")
+	}
+	subdomain := ""
+	if svc, ok := sdk.GetOption[happydns.ServiceMessage](opts, OptionService); ok {
+		subdomain = strings.TrimSuffix(svc.Domain, ".")
+	}
+	origin := sdk.JoinRelative(subdomain, apex)
+	host, ips := addressesFromServer(server, origin)
+	if host == "" {
+		host = origin
+	}
 	// abstract.Server only pins one A and one AAAA. Resolve the host to
 	// pick up any additional records the authoritative DNS exposes, so
 	// multi-IP deployments aren't silently under-probed. Failures are
diff --git a/checker/definition.go b/checker/definition.go
index 74b1a3f..0aeaffa 100644
--- a/checker/definition.go
+++ b/checker/definition.go
@@ -82,6 +82,12 @@ func (p *httpProvider) Definition() *sdk.CheckerDefinition {
 					AutoFill: sdk.AutoFillService,
 					Hide:     true,
 				},
+				{
+					Id:       OptionDomainName,
+					Label:    "Parent domain name",
+					AutoFill: sdk.AutoFillDomainName,
+					Hide:     true,
+				},
 			},
 		},
 		Rules: Rules(),
diff --git a/checker/provider_test.go b/checker/provider_test.go
index feb9f0c..86a5bf0 100644
--- a/checker/provider_test.go
+++ b/checker/provider_test.go
@@ -227,7 +227,7 @@ func TestAddressesFromServer(t *testing.T) {
 	}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
-			host, ips := addressesFromServer(c.srv)
+			host, ips := addressesFromServer(c.srv, "")
 			if host != c.wantHost {
 				t.Errorf("host = %q, want %q", host, c.wantHost)
 			}
diff --git a/checker/service.go b/checker/service.go
index f4fbb9c..0ec5c87 100644
--- a/checker/service.go
+++ b/checker/service.go
@@ -9,7 +9,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"net"
-	"strings"
 
 	sdk "git.happydns.org/checker-sdk-go/checker"
 	happydns "git.happydns.org/happyDomain/model"
@@ -36,15 +35,17 @@ func resolveServer(opts sdk.CheckerOptions) (*abstract.Server, error) {
 	return &server, nil
 }
 
-// addressesFromServer returns the (host, ips) tuple to probe.
-func addressesFromServer(server *abstract.Server) (host string, ips []string) {
+// addressesFromServer returns the (host, ips) tuple to probe. origin is
+// the service's parent zone; the A/AAAA Hdr.Name is relative to it as
+// happyDomain encodes service owners, so we must join before using as FQDN.
+func addressesFromServer(server *abstract.Server, origin string) (host string, ips []string) {
 	if server.A != nil && len(server.A.A) > 0 {
-		host = strings.TrimSuffix(server.A.Hdr.Name, ".")
+		host = sdk.JoinRelative(server.A.Hdr.Name, origin)
 		ips = append(ips, server.A.A.String())
 	}
 	if server.AAAA != nil && len(server.AAAA.AAAA) > 0 {
 		if host == "" {
-			host = strings.TrimSuffix(server.AAAA.Hdr.Name, ".")
+			host = sdk.JoinRelative(server.AAAA.Hdr.Name, origin)
 		}
 		ips = append(ips, server.AAAA.AAAA.String())
 	}
diff --git a/checker/types.go b/checker/types.go
index 2c11eac..142c653 100644
--- a/checker/types.go
+++ b/checker/types.go
@@ -24,6 +24,7 @@ const ObservationKeyHTTP = "http"
 
 const (
 	OptionService           = "service"
+	OptionDomainName        = "domain_name"
 	OptionProbeTimeoutMs    = "probeTimeoutMs"
 	OptionMaxRedirects      = "maxRedirects"
 	OptionUserAgent         = "userAgent"