1 files changed, 6 insertions, 3 deletions
diff --git a/mcs/class/corlib/System.Text/Decoder.cs b/mcs/class/corlib/System.Text/Decoder.cs
index fe715c33796..cf2e6f23efc 100644
--- a/mcs/class/corlib/System.Text/Decoder.cs
+++ b/mcs/class/corlib/System.Text/Decoder.cs
@@ -149,7 +149,10 @@ public abstract class Decoder
 		out int bytesUsed, out int charsUsed, out bool completed)
 	{
 		CheckArguments (bytes, byteIndex, byteCount);
-		CheckArguments (chars, charIndex);
+		if (chars == null)
+			throw new ArgumentNullException ("chars");
+		if (charIndex < 0)
+			throw new ArgumentOutOfRangeException ("charIndex");
 		if (charCount < 0 || chars.Length < charIndex + charCount)
 			throw new ArgumentOutOfRangeException ("charCount");
 
@@ -169,7 +172,7 @@ public abstract class Decoder
 	{
 		if (chars == null)
 			throw new ArgumentNullException ("chars");
-		if (charIndex < 0 || chars.Length <= charIndex)
+		if (charIndex < 0 || chars.Length < charIndex)
 			throw new ArgumentOutOfRangeException ("charIndex");
 	}
 
@@ -177,7 +180,7 @@ public abstract class Decoder
 	{
 		if (bytes == null)
 			throw new ArgumentNullException ("bytes");
-		if (byteIndex < 0 || bytes.Length <= byteIndex)
+		if (byteIndex < 0)
 			throw new ArgumentOutOfRangeException ("byteIndex");
 		if (byteCount < 0 || bytes.Length < byteIndex + byteCount)
 			throw new ArgumentOutOfRangeException ("byteCount");