diff --git a/dotnet/IEC61850forCSharp/MmsValue.cs b/dotnet/IEC61850forCSharp/MmsValue.cs
index 3b5e06ee..d262688a 100644
--- a/dotnet/IEC61850forCSharp/MmsValue.cs
+++ b/dotnet/IEC61850forCSharp/MmsValue.cs
@@ -174,7 +174,13 @@ namespace IEC61850
 			[DllImport("iec61850", CallingConvention = CallingConvention.Cdecl)]
 			static extern UInt16 MmsValue_getOctetStringMaxSize(IntPtr self);
 
-			[DllImport("iec61850", CallingConvention = CallingConvention.Cdecl)]
+            [DllImport("iec61850", CallingConvention = CallingConvention.Cdecl)]
+            static extern byte MmsValue_getOctetStringOctet(IntPtr self, int pos);
+
+            [DllImport("iec61850", CallingConvention = CallingConvention.Cdecl)]
+            static extern void MmsValue_setOctetStringOctet(IntPtr self, int pos, byte value);
+
+            [DllImport("iec61850", CallingConvention = CallingConvention.Cdecl)]
 			static extern IntPtr MmsValue_getOctetStringBuffer(IntPtr self);
 
             [DllImport("iec61850", CallingConvention = CallingConvention.Cdecl)]
@@ -518,6 +524,11 @@ namespace IEC61850
 					throw new MmsValueException ("Operation not supported for this type");
 			}
 
+            /// <summary>
+            /// Sets the value of an octet string by a byte array
+            /// </summary>
+            /// <param name="octetString">Byte array containing the bytes of the octet string.</param>
+            /// <exception cref="MmsValueException">This exception is thrown if the value has the wrong type or the byte array is too large.</exception>
 			public void setOctetString (byte[] octetString)
 			{
 				if (GetType () == MmsType.MMS_OCTET_STRING) {
@@ -531,6 +542,26 @@ namespace IEC61850
 					throw new MmsValueException ("Operation not supported for this type");
 			}
 
+            /// <summary>
+            /// Gets the octet string octet.
+            /// </summary>
+            /// <returns>The octet string octet.</returns>
+            /// <param name="pos">Position of the octet in the octet string.</param>
+            public byte GetOctetStringOctet(int pos)
+            {
+                return MmsValue_getOctetStringOctet(valueReference, pos);
+            }
+
+            /// <summary>
+            /// Sets the octet string octet.
+            /// </summary>
+            /// <param name="pos">Position of the octet in the octet string.</param>
+            /// <param name="value">The octet string octet.</param>
+            public void SetOctetStringOctet(int pos, byte value)
+            {
+                MmsValue_setOctetStringOctet(valueReference, pos, value);
+            }
+
             /// <summary>
             /// Get an element of an array or structure
             /// </summary>
diff --git a/src/mms/iso_mms/common/mms_value.c b/src/mms/iso_mms/common/mms_value.c
index 0da7a196..1281c8a8 100644
--- a/src/mms/iso_mms/common/mms_value.c
+++ b/src/mms/iso_mms/common/mms_value.c
@@ -1429,7 +1429,7 @@ MmsValue_setOctetString(MmsValue* self, const uint8_t* buf, int size)
 void
 MmsValue_setOctetStringOctet(MmsValue* self, int octetPos, uint8_t value)
 {
-    if (octetPos < self->value.octetString.maxSize) {
+    if ((octetPos >= 0) && (octetPos < self->value.octetString.maxSize)) {
         self->value.octetString.buf[octetPos] = value;
 
         if (octetPos >= self->value.octetString.size) {
@@ -1460,9 +1460,11 @@ uint8_t
 MmsValue_getOctetStringOctet(MmsValue* self, int octetPos)
 {
     uint8_t octet = 0x00; /* default value, for out of range request */
+
     if (octetPos < self->value.octetString.size) {
         octet = self->value.octetString.buf[octetPos];
     }
+
     return octet;
 }