diff --git a/server/train-ai/DatasetFetcher.mjs b/server/train-ai/DatasetFetcher.mjs
index 8fc79a4..afd0cce 100644
--- a/server/train-ai/DatasetFetcher.mjs
+++ b/server/train-ai/DatasetFetcher.mjs
@@ -30,19 +30,18 @@ class DatasetFetcher {
 		let iterator = gateway_id == null ? this.repo_rssi.iterate() : this.repo_rssi.iterate_gateway(gateway_id);
 		// Add the readings where we did get a signal
 		for(let rssi of iterator) {
-			if(gateway_id == null)
-				gateway_location = this.repo_gateway.get_by_id(rssi.gateway_id);
 			
 			let item = {
 				input: {
 					latitude: rssi.latitude,
-					longitude: rssi.longitude,
-					distance: haversine(gateway_location, rssi)
+					longitude: rssi.longitude
 				},
 				output: [
 					rssi.rssi
 				]
 			};
+			if(gateway_id !== null)
+				item.input.distance = haversine(gateway_location, rssi);
 			if(extended) {
 				item.ext = {
 					gateway: rssi.gateway_id,
@@ -57,11 +56,13 @@ class DatasetFetcher {
 			let item = {
 				input: {
 					latitude: reading.latitude,
-					longitude: reading.longitude,
-					distance: haversine(gateway_location, reading)
+					longitude: reading.longitude
 				},
 				output: [ -150 ]
 			};
+			if(gateway_id !== null)
+				item.input.distance = haversine(gateway_location, reading);
+			
 			if(extended) {
 				item.ext = {
 					gateway: "(none)",
@@ -89,15 +90,17 @@ class DatasetFetcher {
 		for(let item of result) {
 			item.input.latitude = normalise_lat(item.input.latitude);
 			item.input.longitude = normalise_lng(item.input.longitude);
-			item.input.distance = normalise_gateway_distance(item.input.distance);
+			if(typeof item.input.distance == "number")
+				item.input.distance = normalise_gateway_distance(item.input.distance);
 			item.output[0] = normalise_rssi(item.output[0]);
 		}
 		
+		// Scan the resulting dataset for invalid items
+		this.scan_for_corruption(result);
+		
 		// Shuffle the dataset
 		shuffle_fisher_yates(result);
 		
-		// Scan the resulting dataset for invalid items
-		this.scan_for_corruption(result);
 		
 		return result;
 	}
@@ -125,7 +128,7 @@ class DatasetFetcher {
 					next_item.input,
 					comp_item.input
 				);
-				if(isNaN(distance))
+				if(Number.isNaN(distance))
 					throw new Error(`Error: Got NaN when checking zapping distance.`);
 				
 				if(distance < max_distance_metres) {
@@ -146,13 +149,9 @@ class DatasetFetcher {
 	scan_for_corruption(dataset) {
 		// Scan the input data to make sure it is't corrupt
 		for(let row of dataset) {
-			if(isNaN(row.output[0]) || isNaN(row.input.latitude) || isNaN(row.input.longitude) || isNaN(row.input.distance)) {
+			if(Number.isNaN(row.output[0]) || Number.isNaN(row.input.latitude) || Number.isNaN(row.input.longitude) || Number.isNaN(row.input.distance)) {
 				console.error(row);
-				throw new Error("Error: Found NaN in input data");
-			}
-			if(typeof row.output[0] !== "number" || typeof row.input.latitude !== "number" || typeof row.input.longitude !== "number" || typeof row.input.distance !== "number") {
-				console.error(row);
-				throw new Error("Error: Found item with an invalid type in the input data");
+				throw new Error("Error: Found invalid value in input data");
 			}
 		}