diff --git a/gui/chatblockmodel.cpp b/gui/chatblockmodel.cpp
index 69a46da..fc82600 100644
--- a/gui/chatblockmodel.cpp
+++ b/gui/chatblockmodel.cpp
@@ -538,20 +538,21 @@ void ChatBlockModel::incrementalAppend(int blockIndex, const QString &line)
         const QString defaultColor = getDefaultTextColor();
         const QString escapedLine = line.toHtmlEscaped();
 
-        if (!block.segments.isEmpty() && block.segments.last().type == BlockSegment::Text
-            && !rs.inFence) {
-            // Append to existing prose segment — strip closing </div>, add newline + content
+        // Only extend the last segment if it is an in-progress prose segment
+        // (identified by its trailing </div>). A finalized code fence segment
+        // ends in </pre> and must not be overwritten.
+        bool canExtend = !block.segments.isEmpty()
+            && block.segments.last().type == BlockSegment::Text
+            && block.segments.last().html.endsWith(QStringLiteral("</div>"));
+
+        if (canExtend) {
             QString &segHtml = block.segments.last().html;
-            // Remove trailing </div> to append
-            if (segHtml.endsWith(QStringLiteral("</div>"))) {
-                segHtml.chop(6);
-                segHtml += '\n' + escapedLine + QStringLiteral("</div>");
-            } else {
-                // Shouldn't happen, but fall back to full rebuild
-                segHtml = escapeForHtml(rs.proseLines.join('\n'));
-            }
+            segHtml.chop(6); // remove trailing </div>
+            segHtml += '\n' + escapedLine + QStringLiteral("</div>");
         } else {
-            // Start a new text segment
+            // Start a new prose segment
+            rs.proseLines.clear();
+            rs.proseLines.append(line);
             BlockSegment seg;
             seg.type = BlockSegment::Text;
             seg.html = QStringLiteral("<div style=\"white-space:pre-wrap;color:") + defaultColor + QStringLiteral("\">")