diff --git a/NEWS.md b/NEWS.md
index e2a18de5..afff6768 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -4,6 +4,7 @@ Red Panda C++ Version 1.0.7
   - enhancement: don't highlight '\' as error
   - enhancement: hide add charset  option in project options dialog's compiler set page, when project compiler set is clang
   - fix: When generating project's makefile for clang, don't add -fexec-charset / -finput-charset command line options
+  - fix: index of the longest line not correctly updated when inputting with auto completion open
 
 Red Panda C++ Version 1.0.6
   - fix: gcc compiler set name is not correct in Linux
diff --git a/RedPandaIDE/qsynedit/SynEdit.cpp b/RedPandaIDE/qsynedit/SynEdit.cpp
index d1891fa0..6aaad345 100644
--- a/RedPandaIDE/qsynedit/SynEdit.cpp
+++ b/RedPandaIDE/qsynedit/SynEdit.cpp
@@ -1131,7 +1131,7 @@ QChar SynEdit::lastNonSpaceChar(int line, int ch)
     return QChar();
 }
 
-void SynEdit::setCaretAndSelection(const BufferCoord &ptCaret, const BufferCoord &ptBefore, const BufferCoord &ptAfter)
+void SynEdit::setCaretAndSelection(const BufferCoord &ptCaret, const BufferCoord &ptSelBegin, const BufferCoord &ptSelEnd)
 {
     SynSelectionMode vOldMode = mActiveSelectionMode;
     incPaintLock();
@@ -1140,8 +1140,8 @@ void SynEdit::setCaretAndSelection(const BufferCoord &ptCaret, const BufferCoord
         decPaintLock();
     });
     internalSetCaretXY(ptCaret);
-    setBlockBegin(ptBefore);
-    setBlockEnd(ptAfter);
+    setBlockBegin(ptSelBegin);
+    setBlockEnd(ptSelEnd);
 }
 
 bool SynEdit::inputMethodOn()
diff --git a/RedPandaIDE/qsynedit/SynEdit.h b/RedPandaIDE/qsynedit/SynEdit.h
index 31d9967c..8106a728 100644
--- a/RedPandaIDE/qsynedit/SynEdit.h
+++ b/RedPandaIDE/qsynedit/SynEdit.h
@@ -238,8 +238,8 @@ public:
     void setCaretXYEx(bool CallEnsureCursorPosVisible, BufferCoord value);
     void setCaretXYCentered(const BufferCoord& value);
     void setCaretAndSelection(const BufferCoord& ptCaret,
-                              const BufferCoord& ptBefore,
-                              const BufferCoord& ptAfter);
+                              const BufferCoord& ptSelBegin,
+                              const BufferCoord& ptSelEnd);
 
     bool inputMethodOn();
 
diff --git a/RedPandaIDE/qsynedit/TextBuffer.cpp b/RedPandaIDE/qsynedit/TextBuffer.cpp
index 28d87d28..b21297b4 100644
--- a/RedPandaIDE/qsynedit/TextBuffer.cpp
+++ b/RedPandaIDE/qsynedit/TextBuffer.cpp
@@ -439,8 +439,12 @@ void SynDocument::putString(int Index, const QString &s, bool notify) {
         int oldColumns = mLines[Index]->fColumns;
         mLines[Index]->fString = s;
         calculateLineColumns(Index);
-        if (oldColumns>mLines[Index]->fColumns)
+        if (mIndexOfLongestLine == Index && oldColumns>mLines[Index]->fColumns )
             mIndexOfLongestLine = -1;
+        else if (mIndexOfLongestLine>=0
+                 && mIndexOfLongestLine<mLines.count()
+                 && mLines[Index]->fColumns > mLines[mIndexOfLongestLine]->fColumns)
+            mIndexOfLongestLine = Index;
         if (notify)
             emit putted(Index,1);
         endUpdate();