diff --git a/src/buttons_effects.c b/src/buttons_effects.c
index 0b678185..f1549f75 100644
--- a/src/buttons_effects.c
+++ b/src/buttons_effects.c
@@ -181,6 +181,7 @@ static int Check_block_constraints(enum IMAGE_MODES mode)
   int block_width = 8, block_height = 8, max_colors = 2;  // default values
   int error_count = 0;
   byte errcol = 17;
+  byte pal_mask;
 
   switch (mode)
   {
@@ -198,9 +199,14 @@ static int Check_block_constraints(enum IMAGE_MODES mode)
       max_colors = 4;
       errcol = 33;
       break;
+    case IMAGE_MODE_MEGADRIVE:
+      max_colors = 16;
+      errcol = 65;
+      break;
     default:
       return -1;  // unsupported mode
   }
+  pal_mask = ~(max_colors - 1);
 
   for (y = 0; y <= Main.image_height - block_height; y += block_height)
   {
@@ -215,11 +221,11 @@ static int Check_block_constraints(enum IMAGE_MODES mode)
         {
           int i;
           byte col = Read_pixel_from_layer(0, x+x2, y+y2);
-          if (mode == IMAGE_MODE_GBC)
+          if (mode == IMAGE_MODE_GBC || mode == IMAGE_MODE_MEGADRIVE)
           {
             if (count == 0)
               c[count++] = col;
-            else if ((col & ~3) != (c[0] & ~3))  // compare palettes
+            else if ((col & pal_mask) != (c[0] & pal_mask))  // compare palettes
             {
               if (Main.backups->Pages->Nb_layers < 2)
                 Add_layer(Main.backups, 1);
@@ -566,6 +572,7 @@ void Button_Constraint_menu(void)
   } modes[] = {
     {IMAGE_MODE_ZX,      "ZX Spectrum",   "2 colors per 8x8 block", 1}, // 256x192
     {IMAGE_MODE_GBC,     "Game Boy Color","4 colors per 8x8 block", 1}, // 160x144 to 256x256
+    {IMAGE_MODE_MEGADRIVE,"Sega MegaDrive","16colors per 8x8 block",1}, // 256x224 to 1024x256
     {IMAGE_MODE_THOMSON, "40col (MO/TO)", "2 colors per 8x1 block", 1}, // 320x200
     {IMAGE_MODE_EGX,     "EGX (CPC)",     "Alternate Mode0/Mode1 ", 0}, // 320x200
     {IMAGE_MODE_EGX2,    "EGX2 (CPC)",    "Alternate Mode1/Mode2 ", 0}, // 640x200
@@ -620,7 +627,7 @@ void Button_Constraint_menu(void)
     }
     else if (clicked_button == 3)
     {
-      if (Selected_Constraint_Mode == IMAGE_MODE_GBC)
+      if (Selected_Constraint_Mode == IMAGE_MODE_GBC || Selected_Constraint_Mode == IMAGE_MODE_MEGADRIVE)
         set_palette = 1;  // activate palette back when switching from GBC
       Selected_Constraint_Mode = Window_attribute2;
       for (i = 0; i < sizeof(modes)/sizeof(modes[0]) ; i++)
@@ -632,7 +639,7 @@ void Button_Constraint_menu(void)
           Display_cursor();
           break;
         }
-      if (Selected_Constraint_Mode == IMAGE_MODE_GBC)
+      if (Selected_Constraint_Mode == IMAGE_MODE_GBC || Selected_Constraint_Mode == IMAGE_MODE_MEGADRIVE)
         set_palette = 0;
     }
     else if (clicked_button == 4) // palette
@@ -714,6 +721,7 @@ void Button_Constraint_menu(void)
           case IMAGE_MODE_ZX:
           case IMAGE_MODE_GBC:
           case IMAGE_MODE_C64HIRES:
+          case IMAGE_MODE_MEGADRIVE:
             Snap_width = 8;
             Snap_height = 8;
             break;
@@ -759,6 +767,13 @@ void Button_Constraint_menu(void)
             Fore_color = 7;
             Back_color = 0;
             break;
+          case IMAGE_MODE_MEGADRIVE:  // 64 colors among 512
+            memset(Main.palette + 64, 0, sizeof(T_Components) * (256 - 64));
+            Main.palette[65].R = 255; // for color clashes
+            First_color_in_palette = 0;
+            Fore_color = 15;
+            Back_color = 0;
+            break;
           case IMAGE_MODE_GBC:  // 32 colors among 32768
             memset(Main.palette + 32, 0, sizeof(T_Components) * (256 - 32));
             Main.palette[33].R = 255; // for color clashes
diff --git a/src/const.h b/src/const.h
index 1b30205b..1ff47794 100644
--- a/src/const.h
+++ b/src/const.h
@@ -631,6 +631,7 @@ enum IMAGE_MODES
   IMAGE_MODE_C64FLI,    ///< C64 Flexible Line Interpretation
   IMAGE_MODE_HGR,       ///< Apple 2 HGR
   IMAGE_MODE_DHGR,      ///< Apple 2 DHGR
+  IMAGE_MODE_MEGADRIVE, ///< Sega Mega Drive / Genesis
 };
 
 /// Circle / Ellipse Modes
diff --git a/src/graph.c b/src/graph.c
index a1ccb365..b314a528 100644
--- a/src/graph.c
+++ b/src/graph.c
@@ -3413,24 +3413,33 @@ done:
 /// Paint a pixel with GBC constraints
 ///
 /// Same 4 color palette for all pixels in a 8x8 block.
+///
+/// Megadrive constraints are nearly the same : same 16 color palette in a 8x8 tile
 static void Pixel_in_screen_gbc_with_opt_preview(word x,word y,byte color,int preview)
 {
   word startx = x & ~7;
   word starty = y & ~7;
   word x2, y2;
   byte palette;
+  byte col_mask, pal_mask;
+
+  if (Main.backups->Pages->Image_mode == IMAGE_MODE_MEGADRIVE)
+    col_mask = 15;
+  else
+    col_mask = 3;
+  pal_mask = ~col_mask;
 
   // first set the pixel
   Pixel_in_screen_layered_with_opt_preview(x,y,color,preview);
-  palette = color & ~3;
+  palette = color & pal_mask;
   // force all pixels of the block to the same palette
   for (y2 = 0; y2 < 8; y2++)
   {
     for (x2 = 0; x2 < 8; x2++)
     {
       byte col = Read_pixel_from_current_layer(startx+x2, starty+y2);
-      if ((col & ~3) != palette)
-        Pixel_in_screen_layered_with_opt_preview(startx+x2, starty+y2, palette | (col & 3), preview);
+      if ((col & pal_mask) != palette)
+        Pixel_in_screen_layered_with_opt_preview(startx+x2, starty+y2, palette | (col & col_mask), preview);
     }
   }
 }
@@ -3912,6 +3921,7 @@ void Update_pixel_renderer(void)
     Pixel_in_current_screen_with_opt_preview = Pixel_in_screen_thomson_with_opt_preview;
     break;
   case IMAGE_MODE_GBC:
+  case IMAGE_MODE_MEGADRIVE:
     Pixel_in_current_screen_with_opt_preview = Pixel_in_screen_gbc_with_opt_preview;
     break;
   case IMAGE_MODE_C64HIRES:
diff --git a/src/helpfile.h b/src/helpfile.h
index 9145126c..f5e457a9 100644
--- a/src/helpfile.h
+++ b/src/helpfile.h
@@ -1946,10 +1946,10 @@ static const T_Help_table helptable_effects[] =
   HELP_TEXT ("")
   HELP_BOLD ("Block modes")
   HELP_TEXT ("ZX Spectrum, Game Boy Color, Thomson MOTO,")
-  HELP_TEXT ("C64 MultiColor, C64 HiRes are modes with")
-  HELP_TEXT ("block constraints. Only a limited count of")
-  HELP_TEXT ("different colors (generaly 2) is allowed in")
-  HELP_TEXT ("a pixel block.")
+  HELP_TEXT ("Mega Drive, C64 MultiColor and C64 HiRes")
+  HELP_TEXT ("are modes with block constraints. Only a")
+  HELP_TEXT ("limited count of different colors is")
+  HELP_TEXT ("allowed in a pixel block.")
   HELP_TEXT ("")
   HELP_BOLD ("Game Boy Color")
   HELP_TEXT ("All pixels within a 8x8 block should be in")
@@ -1962,6 +1962,15 @@ static const T_Help_table helptable_effects[] =
   HELP_TEXT ("Color #0 of each palette is transparent for")
   HELP_TEXT ("Game Boy sprites.")
   HELP_TEXT ("")
+  HELP_BOLD ("Sega Mega Drive / Genesis")
+  HELP_TEXT ("The constraints are similar to GBC mode,")
+  HELP_TEXT ("there are 4 palettes of 16 colors each.")
+  HELP_TEXT ("Color #0 of each palette is transparent.")
+  HELP_TEXT ("")
+  HELP_BOLD ("ZX Spectrum")
+  HELP_TEXT ("The two colors of the 8x8 block must share")
+  HELP_TEXT ("the same bightness bit.")
+  HELP_TEXT ("")
   HELP_TEXT ("")
   HELP_BOLD ("C64 Flexible Line Interpretation (FLI)")
   HELP_TEXT ("- Layer 1 contains the background colors,")
diff --git a/src/oldies.c b/src/oldies.c
index 7b04c19b..fe3e7a58 100644
--- a/src/oldies.c
+++ b/src/oldies.c
@@ -65,7 +65,8 @@ static const struct {
   { IMAGE_MODE_C64MULTI,  "C64_MULTICOLOR" },
   { IMAGE_MODE_C64FLI,    "C64_FLI" },
   { IMAGE_MODE_HGR,       "APPLE2_HGR" },
-  { IMAGE_MODE_DHGR,      "APPLE2_DHGR" }
+  { IMAGE_MODE_DHGR,      "APPLE2_DHGR" },
+  { IMAGE_MODE_MEGADRIVE, "SEGAMEGADRIVE" },
 };
 
 const char * Constraint_mode_label(enum IMAGE_MODES mode)