diff --git a/toonz/sources/include/toonz/fill.h b/toonz/sources/include/toonz/fill.h
index 075bebb8..5a4eece2 100644
--- a/toonz/sources/include/toonz/fill.h
+++ b/toonz/sources/include/toonz/fill.h
@@ -27,6 +27,7 @@ public:
   bool m_shiftFill;
   TPoint m_p;
   TPalette *m_palette;
+  bool m_prevailing;
 
   FillParameters()
       : m_styleId(0)
@@ -37,7 +38,8 @@ public:
       , m_maxFillDepth(0)
       , m_p()
       , m_shiftFill(false)
-      , m_palette(0) {}
+      , m_palette(0)
+      , m_prevailing(true) {}
   FillParameters(const FillParameters &params)
       : m_styleId(params.m_styleId)
       , m_fillType(params.m_fillType)
@@ -47,7 +49,8 @@ public:
       , m_maxFillDepth(params.m_maxFillDepth)
       , m_p(params.m_p)
       , m_shiftFill(params.m_shiftFill)
-      , m_palette(params.m_palette) {}
+      , m_palette(params.m_palette)
+      , m_prevailing(params.m_prevailing) {}
 };
 
 //=============================================================================
diff --git a/toonz/sources/toonzlib/fill.cpp b/toonz/sources/toonzlib/fill.cpp
index 9f0a25ed..902a853b 100644
--- a/toonz/sources/toonzlib/fill.cpp
+++ b/toonz/sources/toonzlib/fill.cpp
@@ -32,9 +32,14 @@ inline TPoint nearestInkNotDiagonal(const TRasterCM32P &r, const TPoint &p) {
 // la riga ridisegnata va da *xa a *xb compresi
 // x1 <= *xa <= *xb <= x2
 // N.B. se non viene disegnato neanche un pixel *xa>*xb
+//
+// "prevailing" is set to false on revert-filling the border of
+// region in the Rectangular, Freehand and Polyline fill procedures
+// in order to make the paint to protlude behind the line.
 
 void fillRow(const TRasterCM32P &r, const TPoint &p, int &xa, int &xb,
-             int paint, TPalette *palette, TTileSaverCM32 *saver) {
+             int paint, TPalette *palette, TTileSaverCM32 *saver,
+             bool prevailing = true) {
   int tone, oldtone;
   TPixelCM32 *pix, *pix0, *limit, *tmp_limit;
 
@@ -49,7 +54,34 @@ void fillRow(const TRasterCM32P &r, const TPoint &p, int &xa, int &xb,
   for (; pix <= limit; pix++) {
     if (pix->getPaint() == paint) break;
     tone = pix->getTone();
-    if (tone > oldtone || tone == 0) break;
+    if (tone == 0) break;
+    // prevent fill area from protruding behind the colored line
+    if (tone > oldtone) {
+      // not-yet-colored line case
+      if (prevailing && !pix->isPurePaint() && pix->getInk() != pix->getPaint())
+        break;
+      while (pix != pix0) {
+        // iterate back in order to leave the pixel with the lowest tone
+        // unpainted
+        pix--;
+        // make the one-pixel-width semi-transparent line to be painted
+        if (prevailing && pix->getInk() != pix->getPaint()) break;
+        if (pix->getTone() > oldtone) {
+          // check if the current pixel is NOT with the lowest tone among the
+          // vertical neighbors as well
+          if (p.y > 0 && p.y < r->getLy() - 1) {
+            TPixelCM32 *upPix   = pix - r->getWrap();
+            TPixelCM32 *downPix = pix + r->getWrap();
+            if (upPix->getTone() > pix->getTone() &&
+                downPix->getTone() > pix->getTone())
+              continue;
+          }
+          break;
+        }
+      }
+      pix++;
+      break;
+    }
     oldtone = tone;
   }
   if (tone == 0) {
@@ -72,7 +104,34 @@ void fillRow(const TRasterCM32P &r, const TPoint &p, int &xa, int &xb,
   for (pix--; pix >= limit; pix--) {
     if (pix->getPaint() == paint) break;
     tone = pix->getTone();
-    if (tone > oldtone || tone == 0) break;
+    if (tone == 0) break;
+    // prevent fill area from protruding behind the colored line
+    if (tone > oldtone) {
+      // not-yet-colored line case
+      if (prevailing && !pix->isPurePaint() && pix->getInk() != pix->getPaint())
+        break;
+      while (pix != pix0) {
+        // iterate forward in order to leave the pixel with the lowest tone
+        // unpainted
+        pix++;
+        // make the one-pixel-width semi-transparent line to be painted
+        if (prevailing && pix->getInk() != pix->getPaint()) break;
+        if (pix->getTone() > oldtone) {
+          // check if the current pixel is NOT with the lowest tone among the
+          // vertical neighbors as well
+          if (p.y > 0 && p.y < r->getLy() - 1) {
+            TPixelCM32 *upPix   = pix - r->getWrap();
+            TPixelCM32 *downPix = pix + r->getWrap();
+            if (upPix->getTone() > pix->getTone() &&
+                downPix->getTone() > pix->getTone())
+              continue;
+          }
+          break;
+        }
+      }
+      pix--;
+      break;
+    }
     oldtone = tone;
   }
   if (tone == 0) {
@@ -234,7 +293,8 @@ bool fill(const TRasterCM32P &r, const FillParameters &params,
   /*- 画面外のクリックの場合はreturn -*/
   if (!bbbox.contains(p)) return false;
   /*- 既に同じ色が塗られている場合はreturn -*/
-  if ((r->pixels(p.y) + p.x)->getPaint() == paint) return false;
+  int paintAtClickedPos = (r->pixels(p.y) + p.x)->getPaint();
+  if (paintAtClickedPos == paint) return false;
   /*- 「透明部分だけを塗る」オプションが有効で、既に色が付いている場合はreturn
    * -*/
   if (params.m_emptyOnly && (r->pixels(p.y) + p.x)->getPaint() != 0)
@@ -252,7 +312,6 @@ bool fill(const TRasterCM32P &r, const FillParameters &params,
   default:
     assert(false);
   }
-
   /*-- 四隅の色を見て、一つでも変わったらsaveBoxを更新する --*/
   TPixelCM32 borderIndex[4];
   TPixelCM32 *borderPix[4];
@@ -271,7 +330,7 @@ bool fill(const TRasterCM32P &r, const FillParameters &params,
 
   std::stack<FillSeed> seeds;
 
-  fillRow(r, p, xa, xb, paint, params.m_palette, saver);
+  fillRow(r, p, xa, xb, paint, params.m_palette, saver, params.m_prevailing);
   seeds.push(FillSeed(xa, xb, y, 1));
   seeds.push(FillSeed(xa, xb, y, -1));
 
@@ -294,8 +353,13 @@ bool fill(const TRasterCM32P &r, const FillParameters &params,
     while (pix <= limit) {
       oldtone = threshTone(*oldpix, fillDepth);
       tone    = threshTone(*pix, fillDepth);
-      if (pix->getPaint() != paint && tone <= oldtone && tone != 0) {
-        fillRow(r, TPoint(x, y), xc, xd, paint, params.m_palette, saver);
+      // the last condition is added in order to prevent fill area from
+      // protruding behind the colored line
+      if (pix->getPaint() != paint && tone <= oldtone && tone != 0 &&
+          (pix->getPaint() != pix->getInk() ||
+           pix->getPaint() == paintAtClickedPos)) {
+        fillRow(r, TPoint(x, y), xc, xd, paint, params.m_palette, saver,
+                params.m_prevailing);
         if (xc < xa) seeds.push(FillSeed(xc, xa - 1, y, -dy));
         if (xd > xb) seeds.push(FillSeed(xb + 1, xd, y, -dy));
         if (oldxd >= xc - 1)
diff --git a/toonz/sources/toonzlib/fillutil.cpp b/toonz/sources/toonzlib/fillutil.cpp
index 9912df76..2d5e9687 100644
--- a/toonz/sources/toonzlib/fillutil.cpp
+++ b/toonz/sources/toonzlib/fillutil.cpp
@@ -69,6 +69,8 @@ void fillArea(const TRasterCM32P &ras, TRegion *r, int colorId,
 void restoreColors(const TRasterCM32P &r,
                    const std::vector<std::pair<TPoint, int>> &seeds) {
   FillParameters params;
+  // in order to make the paint to protlude behind the line
+  params.m_prevailing = false;
   for (UINT i = 0; i < seeds.size(); i++) {
     params.m_p       = seeds[i].first;
     params.m_styleId = seeds[i].second;
@@ -232,6 +234,8 @@ void AreaFiller::rectFill(const TRect &rect, int color, bool onlyUnfilled,
   // fillate.
   count1 = 0;
   FillParameters params;
+  // in order to make the paint to protlude behind the line
+  params.m_prevailing = false;
   if (r.x0 > 0)
     for (y = r.y0; y <= r.y1; y++) {
       params.m_p       = TPoint(r.x0, y);