diff --git a/src/UKHASExtractor.cxx b/src/UKHASExtractor.cxx
index a640163..41049f4 100644
--- a/src/UKHASExtractor.cxx
+++ b/src/UKHASExtractor.cxx
@@ -320,18 +320,19 @@ static void attempt_settings(Json::Value &data, const Json::Value &sentence,
                              const string &checksum_name,
                              const vector<string> &parts)
 {
-    if (!sentence.isObject())
-        throw runtime_error("Invalid configuration (sentence not an object)");
+    if (!sentence.isObject() || !sentence["callsign"].isString() ||
+        !sentence["fields"].isArray() || !sentence["fields"].size())
+        throw runtime_error("Invalid configuration "
+                                "(missing callsign or fields)");
 
-    const Json::Value &fields = sentence["fields"];
-
-    const string callsign = sentence["payload"].asString();
-    if (parts[0] != callsign)
+    if (sentence["callsign"] != parts[0])
         throw runtime_error("Incorrect callsign");
 
     if (sentence["checksum"] != checksum_name)
         throw runtime_error("Wrong checksum type");
 
+    const Json::Value &fields = sentence["fields"];
+
     if (fields.size() != (parts.size() - 1))
         throw runtime_error("Incorrect number of fields");
 
diff --git a/tests/test_extractor.py b/tests/test_extractor.py
index 59c19cb..74f3063 100644
--- a/tests/test_extractor.py
+++ b/tests/test_extractor.py
@@ -233,7 +233,7 @@ class TestUKHASExtractor:
 
     crude_parse_flight_doc = {
         "sentences": [ {
-            "payload": "TESTING",
+            "callsign": "TESTING",
             "checksum": "crc16-ccitt",
             "fields": [
                 {"name": "field_a"},
@@ -281,10 +281,10 @@ class TestUKHASExtractor:
 
     multi_config_flight_doc = {
         "sentences": [
-            { "payload": "AWKWARD",
+            { "callsign": "AWKWARD",
               "checksum": "crc16-ccitt",
               "fields": [ {"name": "fa"}, {"name": "fo"}, {"name": "fc"} ] },
-            { "payload": "AWKWARD",
+            { "callsign": "AWKWARD",
               "checksum": "crc16-ccitt",
               "fields": [ {"name": "fa"}, {"name": "fb"} ] }
         ]
@@ -312,7 +312,7 @@ class TestUKHASExtractor:
 
     ddmmmmmm_flight_doc = {
         "sentences": [ {
-            "payload": "TESTING",
+            "callsign": "TESTING",
             "checksum": "crc16-ccitt",
             "fields": [
                 {"sensor":"stdtelem.coordinate","name":"lat_a",