diff --git a/runelite-client/src/main/java/net/runelite/client/rs/ClientConfigLoader.java b/runelite-client/src/main/java/net/runelite/client/rs/ClientConfigLoader.java
index 29459d9e7f..ed105ec830 100644
--- a/runelite-client/src/main/java/net/runelite/client/rs/ClientConfigLoader.java
+++ b/runelite-client/src/main/java/net/runelite/client/rs/ClientConfigLoader.java
@@ -55,11 +55,15 @@ class ClientConfigLoader
 
 		final RSConfig config = new RSConfig();
 
-		try (final Response response = RuneLiteAPI.CLIENT.newCall(request).execute();
-			final BufferedReader in = new BufferedReader(new InputStreamReader(response.body().byteStream())))
+		try (final Response response = RuneLiteAPI.CLIENT.newCall(request).execute())
 		{
-			String str;
+			if (!response.isSuccessful())
+			{
+				throw new IOException("Unsuccessful response: " + response.message());
+			}
 
+			String str;
+			final BufferedReader in = new BufferedReader(new InputStreamReader(response.body().byteStream()));
 			while ((str = in.readLine()) != null)
 			{
 				int idx = str.indexOf('=');
diff --git a/runelite-client/src/main/java/net/runelite/client/rs/ClientLoader.java b/runelite-client/src/main/java/net/runelite/client/rs/ClientLoader.java
index f6c77916c4..dbd2c0c95e 100644
--- a/runelite-client/src/main/java/net/runelite/client/rs/ClientLoader.java
+++ b/runelite-client/src/main/java/net/runelite/client/rs/ClientLoader.java
@@ -26,6 +26,7 @@
  */
 package net.runelite.client.rs;
 
+import com.google.common.base.Strings;
 import com.google.common.hash.Hashing;
 import com.google.common.io.ByteStreams;
 import com.google.common.reflect.TypeToken;
@@ -110,6 +111,12 @@ public class ClientLoader implements Supplier<Applet>
 				try
 				{
 					config = ClientConfigLoader.fetch(host);
+
+					if (Strings.isNullOrEmpty(config.getCodeBase()) || Strings.isNullOrEmpty(config.getInitialJar()) || Strings.isNullOrEmpty(config.getInitialClass()))
+					{
+						throw new IOException("Invalid or missing jav_config");
+					}
+
 					break;
 				}
 				catch (IOException e)