diff --git a/S7.Net/PlcAsynchronous.cs b/S7.Net/PlcAsynchronous.cs
index 26cf05c..868ddb1 100644
--- a/S7.Net/PlcAsynchronous.cs
+++ b/S7.Net/PlcAsynchronous.cs
@@ -39,11 +39,16 @@ namespace S7.Net
             var s7data = await COTP.TSDU.ReadAsync(stream);
             if (s7data == null)
                 throw new WrongNumberOfBytesException("No data received in response to Communication Setup");
+            if (s7data.Length < 2)
+                throw new WrongNumberOfBytesException("Not enough data received in response to Communication Setup");
 
             //Check for S7 Ack Data
             if (s7data[1] != 0x03)
                 throw new InvalidDataException("Error reading Communication Setup response", s7data, 1, 0x03);
 
+            if (s7data.Length < 20)
+                throw new WrongNumberOfBytesException("Not enough data received in response to Communication Setup");
+
             MaxPDUSize = (short)(s7data[18] * 256 + s7data[19]);
         }
 
diff --git a/S7.Net/PlcSynchronous.cs b/S7.Net/PlcSynchronous.cs
index 34fa143..7cb37f4 100644
--- a/S7.Net/PlcSynchronous.cs
+++ b/S7.Net/PlcSynchronous.cs
@@ -34,11 +34,16 @@ namespace S7.Net
                 var s7data = COTP.TSDU.Read(stream);
                 if (s7data == null)
                     throw new WrongNumberOfBytesException("No data received in response to Communication Setup");
+                if (s7data.Length < 2)
+                    throw new WrongNumberOfBytesException("Not enough data received in response to Communication Setup");
 
                 //Check for S7 Ack Data
                 if (s7data[1] != 0x03)
                     throw new InvalidDataException("Error reading Communication Setup response", s7data, 1, 0x03);
 
+                if (s7data.Length < 20)
+                    throw new WrongNumberOfBytesException("Not enough data received in response to Communication Setup");
+
                 MaxPDUSize = (short)(s7data[18] * 256 + s7data[19]);
             }
             catch (Exception exc)