diff --git a/Assets/PerfectWorld/Scripts/Network/CSNetwork/Security/StreamCompress.cs b/Assets/PerfectWorld/Scripts/Network/CSNetwork/Security/StreamCompress.cs
index 12fb2deb35..7b327c9974 100644
--- a/Assets/PerfectWorld/Scripts/Network/CSNetwork/Security/StreamCompress.cs
+++ b/Assets/PerfectWorld/Scripts/Network/CSNetwork/Security/StreamCompress.cs
@@ -93,6 +93,34 @@ namespace CSNetwork.Security
             }
         }
 
+        // Copy bytes from history using MPPC's 8 KB circular window semantics.
+        // Source starts at (historyPos - offset) modulo window size and may overlap
+        // destination; freshly written bytes must be visible to subsequent reads.
+        private void CopyFromHistoryCircular(int offset, int length)
+        {
+            int srcPos = historyPos - offset;
+            if (srcPos < 0)
+                srcPos += MPPC_HIST_LEN; // wrap source into window
+
+            int dstPos = historyPos;
+
+            while (length-- > 0)
+            {
+                history[dstPos] = history[srcPos];
+
+                dstPos++;
+                if (dstPos == MPPC_HIST_LEN)
+                    dstPos = 0; // wrap destination
+
+                srcPos++;
+                if (srcPos == MPPC_HIST_LEN)
+                    srcPos = 0; // wrap source
+            }
+
+            // Advance history head to the end of the copied sequence
+            historyPos = dstPos;
+        }
+
         public Octets Update(Octets input)
         {
             // Add input to legacy buffer
@@ -288,13 +316,19 @@ namespace CSNetwork.Security
                     break;
                 }
 
-                if (historyPos - (int)offset < 0 || historyPos + (int)length > MPPC_HIST_LEN)
+                // Perform match copy in the 8 KB circular history buffer.
+                // Valid offsets are in 1..MPPC_HIST_LEN; offset==0 would be EOB (handled above).
+                if (offset == 0 || offset > MPPC_HIST_LEN)
+                {
+                    // Invalid backreference relative to the sliding window; defer until more data
+                    // by restoring bit/read positions to the last safe checkpoint.
+                    bitPos = adjust_bitPos;
+                    readPos = adjust_readPos;
                     break;
+                }
 
-                LameCopy(historyPos, historyPos - (int)offset, (int)length);
-                historyPos += (int)length;
-                if (historyPos >= MPPC_HIST_LEN)
-                    historyPos = 0;
+                // Circular, overlap-safe copy as required by MPPC (LZ77-style) semantics.
+                CopyFromHistoryCircular((int)offset, (int)length);
             }
 
             // Copy remaining history segment to output