diff --git a/src/core/varlink-unit.c b/src/core/varlink-unit.c
index 964efa3534..c90ff987e8 100644
--- a/src/core/varlink-unit.c
+++ b/src/core/varlink-unit.c
@@ -753,7 +753,8 @@ typedef struct StartTransientContextParameters {
         const char *description;
         TransientExecContextParameters exec;
         TransientServiceParameters service;
-        const char *bad_exec_field; /* Set by inner Exec dispatcher to the unknown sub-property name */
+        const char *bad_exec_field;    /* Set by inner Exec dispatcher to the unknown sub-property name */
+        const char *bad_service_field;
 } StartTransientContextParameters;
 
 static void start_transient_context_parameters_done(StartTransientContextParameters *p) {
@@ -885,7 +886,7 @@ static int dispatch_transient_service(const char *name, sd_json_variant *variant
 
         StartTransientContextParameters *p = ASSERT_PTR(userdata);
         p->service.present = true;
-        return sd_json_dispatch(variant, service_dispatch, /* flags= */ 0, &p->service);
+        return sd_json_dispatch_full(variant, service_dispatch, /* bad= */ NULL, /* flags= */ 0, &p->service, &p->bad_service_field);
 }
 
 static int dispatch_transient_context(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata) {
@@ -911,6 +912,8 @@ static int dispatch_transient_context(const char *name, sd_json_variant *variant
                  * actual sub-property. */
                 if (streq(bad_field, "Exec") && !isempty(p->context.bad_exec_field))
                         p->unsupported_property = strjoin("Exec.", p->context.bad_exec_field);
+                else if (streq(bad_field, "Service") && !isempty(p->context.bad_service_field))
+                        p->unsupported_property = strjoin("Service.", p->context.bad_service_field);
                 else
                         p->unsupported_property = strdup(bad_field);
                 if (!p->unsupported_property)
diff --git a/test/units/TEST-26-SYSTEMCTL.sh b/test/units/TEST-26-SYSTEMCTL.sh
index a98ef7646d..d489cc3ec8 100755
--- a/test/units/TEST-26-SYSTEMCTL.sh
+++ b/test/units/TEST-26-SYSTEMCTL.sh
@@ -690,8 +690,17 @@ varlinkctl call "$MANAGER_SOCKET" io.systemd.Unit.StartTransient \
     '{"context":{"ID":"varlink-transient-exec.slice","Exec":{"WorkingDirectory":{"path":"/tmp","missingOK":false}}}}' |& grep "io.systemd.Unit.UnitTypeNotSupported"
 # Unknown field in Exec is rejected as PropertyNotSupported
 defer_transient_cleanup varlink-transient-unknown-exec.service
-varlinkctl call "$MANAGER_SOCKET" io.systemd.Unit.StartTransient \
-    '{"context":{"ID":"varlink-transient-unknown-exec.service","Exec":{"RootDirectory":"/tmp"},"Service":{"Type":"oneshot","ExecStart":[{"path":"/bin/true"}]}}}' |& grep "io.systemd.Unit.PropertyNotSupported"
+unsupported_exec=$(varlinkctl call "$MANAGER_SOCKET" io.systemd.Unit.StartTransient \
+    '{"context":{"ID":"varlink-transient-unknown-exec.service","Exec":{"RootDirectory":"/tmp"},"Service":{"Type":"oneshot","ExecStart":[{"path":"/bin/true"}]}}}' 2>&1 || true)
+echo "$unsupported_exec" | grep "io.systemd.Unit.PropertyNotSupported"
+echo "$unsupported_exec" | grep "Exec.RootDirectory"
+# Service field declared in the IDL but not yet settable at creation is rejected as PropertyNotSupported,
+# and the offending sub-property is identified
+defer_transient_cleanup varlink-transient-unknown-service.service
+unsupported_service=$(varlinkctl call "$MANAGER_SOCKET" io.systemd.Unit.StartTransient \
+    '{"context":{"ID":"varlink-transient-unknown-service.service","Service":{"Type":"oneshot","Restart":"always","ExecStart":[{"path":"/bin/true"}]}}}' 2>&1 || true)
+echo "$unsupported_service" | grep "io.systemd.Unit.PropertyNotSupported"
+echo "$unsupported_service" | grep "Service.Restart"
 set -o pipefail
 
 transient_cleanup