diff --git a/brush.c b/brush.c
index 3af71d4f..503ee6b4 100644
--- a/brush.c
+++ b/brush.c
@@ -914,6 +914,7 @@ void Outline_brush(void)
     Brush_offset_Y=(Brush_height>>1);
 
     free(temp); // Libération de l'ancienne brosse
+    temp = NULL;
 
     // Réallocation d'un buffer de Smear
     free(Smear_brush);
@@ -1026,6 +1027,7 @@ void Nibble_brush(void)
       Brush_offset_Y=(Brush_height>>1);
 
       free(temp); // Libération de l'ancienne brosse
+      temp = NULL;
 
       // Réallocation d'un buffer de Smear
       free(Smear_brush);
@@ -1196,6 +1198,7 @@ void Stretch_brush(short x1, short y1, short x2, short y2)
 
   // Free some memory
   free(Smear_brush);
+  Smear_brush = NULL;
 
   if ((new_brush=((byte *)malloc(new_brush_width*new_brush_height))))
   {
@@ -1507,6 +1510,7 @@ void Distort_brush(short x1, short y1, short x2, short y2, short x3, short y3, s
     // Out of memory while allocating new brush
     Error(0);
     free(new_smear_brush);
+    new_smear_brush = NULL;
     return;
   }
 
@@ -1767,6 +1771,8 @@ void Compute_quad_texture(int x1,int y1,int xt1,int yt1,
   free(ScanY_Yt[1]);
   free(ScanY_X[0]);
   free(ScanY_X[1]);
+
+  ScanY_Xt[0] = ScanY_Xt[1] = ScanY_Yt[0] = ScanY_Yt[1] = ScanY_X[0] = ScanY_X[1] = NULL;
 }
 
 
@@ -1807,6 +1813,7 @@ void Rotate_brush(float angle)
   new_brush_height=y_max+1-y_min;
 
   free(Smear_brush); // On libère un peu de mémoire
+  Smear_brush = NULL;
 
   if ((new_brush=((byte *)malloc(new_brush_width*new_brush_height))))
   {
@@ -1929,6 +1936,8 @@ void Draw_quad_texture_preview(int x1,int y1,int xt1,int yt1,
   free(ScanY_Yt[1]);
   free(ScanY_X[0]);
   free(ScanY_X[1]);
+
+  ScanY_Xt[0] = ScanY_Xt[1] = ScanY_Yt[0] = ScanY_Yt[1] = ScanY_X[0] = ScanY_X[1] = NULL;
 }
 
 
diff --git a/brush_ops.c b/brush_ops.c
index 8178a573..c1227d55 100644
--- a/brush_ops.c
+++ b/brush_ops.c
@@ -507,6 +507,7 @@ void Polybrush_12_8(void)
 
     Capture_brush_with_lasso(Polyfill_number_of_points,Polyfill_table_of_points,click==RIGHT_SIDE);
     free(Polyfill_table_of_points);
+    Polyfill_table_of_points = NULL;
 
     // On raffiche l'écran pour effacer les traits en xor et pour raffraichir
     // l'écran si on a découpé une partie de l'image en prenant la brosse.
diff --git a/engine.c b/engine.c
index 955af5e1..ef958885 100644
--- a/engine.c
+++ b/engine.c
@@ -1988,6 +1988,7 @@ void Close_popup(void)
   else
   {
     free(Window_background[Windows_open-1]);
+    Window_background[Windows_open-1] = NULL;
     Windows_open--;
   
     Paintbrush_hidden=Paintbrush_hidden_before_window;
diff --git a/fileformats.c b/fileformats.c
index 62f8b5c6..2244b8e5 100644
--- a/fileformats.c
+++ b/fileformats.c
@@ -125,6 +125,7 @@ void Load_IMG(T_IO_Context * context)
       }
 
       free(buffer);
+      buffer = NULL;
     }
     else
       File_error=1;
@@ -642,6 +643,7 @@ void Load_LBM(T_IO_Context * context)
                         File_error=2;
                     }
                     free(LBM_buffer);
+                    LBM_buffer = NULL;
                   }
                   else
                   {                                               // compressé
@@ -684,6 +686,7 @@ void Load_LBM(T_IO_Context * context)
                     }
 
                     free(LBM_buffer);
+                    LBM_buffer = NULL;
                     /*Close_lecture();*/
                   }
                 }
@@ -703,6 +706,7 @@ void Load_LBM(T_IO_Context * context)
                         File_error=2;
                     }
                     free(LBM_buffer);
+                    LBM_buffer = NULL;
                   }
                   else
                   {                                               // compressé
@@ -1200,6 +1204,7 @@ void Load_BMP(T_IO_Context * context)
                     File_error=2;
                 }
                 free(buffer);
+                buffer = NULL;
                 break;
 
               case 1 : // Compression RLE 8 bits
@@ -1418,6 +1423,7 @@ void Load_BMP(T_IO_Context * context)
             
           }
           free(buffer);
+          buffer = NULL;
           fclose(file);
         }
       }
@@ -2020,6 +2026,7 @@ void Load_GIF(T_IO_Context * context)
       free(alphabet_suffix);
       free(alphabet_prefix);
       free(alphabet_stack);
+      alphabet_suffix = alphabet_prefix = alphabet_stack = NULL;
     } // Le fichier contenait au moins la signature GIF87a ou GIF89a
     else
       File_error=1;
@@ -2759,6 +2766,7 @@ void Load_PCX(T_IO_Context * context)
             }
 
             free(LBM_buffer);
+            LBM_buffer = NULL;
           }
         }
       }
@@ -2834,6 +2842,7 @@ void Load_PCX(T_IO_Context * context)
             /*Close_lecture();*/
           }
           free(buffer);
+          buffer = NULL;
         }
       }
     }
@@ -3086,6 +3095,7 @@ void Load_SCx(T_IO_Context * context)
             }
           }
           free(LBM_buffer);
+          LBM_buffer = NULL;
         }
         else
           File_error=1;
@@ -3376,6 +3386,7 @@ void Load_PNG(T_IO_Context * context)
                       context->Palette[x].B=palette[x].blue;
                     }
                     free(palette);
+                    palette = NULL;
                   }
                   
                   if (color_type != PNG_COLOR_TYPE_RGB && color_type != PNG_COLOR_TYPE_RGB_ALPHA)
@@ -3452,10 +3463,14 @@ void Load_PNG(T_IO_Context * context)
                   /* cleanup heap allocation */
                   if (row_pointers_allocated)
                   {
-                    for (y=0; y<context->Height; y++)
+                    for (y=0; y<context->Height; y++) {
                       free(Row_pointers[y]);
+                      Row_pointers[y] = NULL;
+                    }
+                      
                   }
                   free(Row_pointers);
+                  Row_pointers = NULL;
                 }
                 else
                   File_error=2;
diff --git a/filesel.c b/filesel.c
index c9346c6d..a3618636 100644
--- a/filesel.c
+++ b/filesel.c
@@ -138,6 +138,7 @@ void Free_fileselector_list(T_Fileselector *list)
     list->First=list->First->Next;
     // Et on efface l'ancien premier élément de la liste
     free(temp_item);
+    temp_item = NULL;
   }
   Recount_files(list);
 }
@@ -325,6 +326,7 @@ void Read_list_of_files(T_Fileselector *list, byte selected_format)
 
   closedir(current_directory);
   free(current_path);
+  current_path = NULL;
 
   Recount_files(list);
 }
@@ -1447,8 +1449,8 @@ byte Button_Load_or_Save(byte load, T_IO_Context *context)
                 break;
                 
               case 0: // Set
-                if (Config.Bookmark_directory[clicked_button-10])
-                  free(Config.Bookmark_directory[clicked_button-10]);
+                free(Config.Bookmark_directory[clicked_button-10]);
+                Config.Bookmark_directory[clicked_button-10] = NULL;
                 Config.Bookmark_label[clicked_button-10][0]='\0';
                 temp=strlen(Main_current_directory);
                 Config.Bookmark_directory[clicked_button-10]=malloc(temp+1);
diff --git a/graph.c b/graph.c
index eec2d93c..98d1bf47 100644
--- a/graph.c
+++ b/graph.c
@@ -2531,6 +2531,7 @@ void Polyfill_general(int vertices, short * points, int color)
   }
 
   free(initial_edge);
+  initial_edge = NULL;
 
   // On ne connait pas simplement les xmin et xmax ici, mais de toutes façon ce n'est pas utilisé en preview
   Update_part_of_screen(0,top,Main_image_width,bottom-top+1);
diff --git a/init.c b/init.c
index e574dbfc..6ae4456d 100644
--- a/init.c
+++ b/init.c
@@ -824,12 +824,14 @@ T_Gui_skin * Load_graphics(const char * skin_file)
   {
     sprintf(Gui_loading_error_message, "Unable to load the skin image (missing? not an image file?)\n");
     free(gfx);
+    gfx = NULL;
     return NULL;
   }
   if (Parse_skin(gui, gfx))
   {
     SDL_FreeSurface(gui);
     free(gfx);
+    gfx = NULL;
     return NULL;
   }
   SDL_FreeSurface(gui);
diff --git a/loadsave.c b/loadsave.c
index 4a0efa36..023e3be5 100644
--- a/loadsave.c
+++ b/loadsave.c
@@ -563,6 +563,7 @@ void End_write(FILE *file)
     if (! Write_bytes(file,Write_buffer,Write_buffer_index))
       File_error=1;
   free(Write_buffer);
+  Write_buffer = NULL;
 }
 
 
@@ -1001,14 +1002,8 @@ byte Get_pixel(T_IO_Context *context, short x, short y)
 /// Cleans up resources (currently: the 24bit buffer) 
 void Destroy_context(T_IO_Context *context)
 {
-  if (context->Buffer_image_24b)
-  {
-    free(context->Buffer_image_24b);
-  }
-  if (context->Buffer_image)
-  {
-    free(context->Buffer_image);
-  }
+  free(context->Buffer_image_24b);
+  free(context->Buffer_image);
   memset(context, 0, sizeof(T_IO_Context));
 }
 
@@ -1243,6 +1238,7 @@ byte Process_backups(T_String_list **list)
     free(files_vector[i]);
   }
   free(files_vector);
+  files_vector = NULL;
   
   return nb_files;
 }
diff --git a/main.c b/main.c
index 058b916d..64fadc6b 100644
--- a/main.c
+++ b/main.c
@@ -373,6 +373,7 @@ int Analyze_command_line(int argc, char * argv[], char *main_filename, char *mai
             Extract_filename(spare_filename, buffer);
           }
           free(buffer);
+          buffer = NULL;
         }
         else
         {
@@ -533,6 +534,7 @@ int Init_program(int argc,char * argv[])
               icon_mask[(y*32+x)/8] |=0x80>>(x&7);
         SDL_WM_SetIcon(icon,icon_mask);
         free(icon_mask);
+        icon_mask = NULL;
       }
 
       SDL_FreeSurface(icon);
@@ -835,23 +837,25 @@ void Program_shutdown(void)
   Delete_safety_backups();
 
   // On libère le buffer de gestion de lignes
-  if(Horizontal_line_buffer) free(Horizontal_line_buffer);
+  free(Horizontal_line_buffer);
+  Horizontal_line_buffer = NULL;
 
   // On libère le pinceau spécial
-  if (Paintbrush_sprite) free(Paintbrush_sprite);
+  free(Paintbrush_sprite);
+  Paintbrush_sprite = NULL;
 
   // On libère les différents écrans virtuels et brosse:
-  if(Brush) free(Brush);
+  free(Brush);
+  Brush = NULL;
   Set_number_of_backups(0);
-  if(Spare_screen) free(Spare_screen);
-  if(Main_screen) free(Main_screen);
+  free(Spare_screen);
+  Spare_screen = NULL;
+  free(Main_screen);
+  Main_screen = NULL;
 
   // Free the skin (Gui graphics) data
-  if (Gfx)
-  {
-    free(Gfx);
-    Gfx=NULL;
-  }
+  free(Gfx);
+  Gfx=NULL;
 
   // On prend bien soin de passer dans le répertoire initial:
   if (chdir(Initial_directory)!=-1)
diff --git a/miscfileformats.c b/miscfileformats.c
index fa67154d..308f3cc7 100644
--- a/miscfileformats.c
+++ b/miscfileformats.c
@@ -1462,6 +1462,7 @@ void Load_PI1(T_IO_Context * context)
       else
         File_error=1;
       free(buffer);
+      buffer = NULL;
     }
     else
       File_error=1;
@@ -1528,6 +1529,7 @@ void Save_PI1(T_IO_Context * context)
     }
     // Libération du buffer mémoire
     free(buffer);
+    buffer = NULL;
   }
   else
   {
@@ -1790,12 +1792,14 @@ void Load_PC1(T_IO_Context * context)
         File_error=1;
       free(bufferdecomp);
       free(buffercomp);
+      buffercomp = bufferdecomp = NULL;
     }
     else
     {
       File_error=1;
       free(bufferdecomp);
       free(buffercomp);
+      buffercomp = bufferdecomp = NULL;
     }
     fclose(file);
   }
@@ -1866,6 +1870,7 @@ void Save_PC1(T_IO_Context * context)
     // Libération des buffers mémoire
     free(bufferdecomp);
     free(buffercomp);
+    buffercomp = bufferdecomp = NULL;
   }
   else
   {
@@ -1969,6 +1974,7 @@ void Load_NEO(T_IO_Context * context)
       else
         File_error=1;
       free(buffer);
+      buffer = NULL;
     }
     else
       File_error=1;
@@ -2033,6 +2039,7 @@ void Save_NEO(T_IO_Context * context)
     }
     // Libération du buffer mémoire
     free(buffer);
+    buffer = NULL;
   }
   else
   {
@@ -2667,6 +2674,7 @@ void Save_SCR(T_IO_Context * context)
 	fclose(file);
 
 	free (output);
+  output = NULL;
 
 	File_error = 0;
 }
diff --git a/op_c.c b/op_c.c
index 28cb68e1..20b41ff3 100644
--- a/op_c.c
+++ b/op_c.c
@@ -223,6 +223,7 @@ void CT_delete(T_Conversion_table * t)
 {
   free(t->table);
   free(t);
+  t = NULL;
 }
 
 
@@ -299,7 +300,7 @@ T_Occurrence_table * OT_new(int nbb_r,int nbb_g,int nbb_b)
     {
       // Not enough memory !
       free(n);
-      n=0;
+      n=NULL;
     }
   }
 
@@ -312,6 +313,7 @@ void OT_delete(T_Occurrence_table * t)
 {
   free(t->table);
   free(t);
+  t = NULL;
 }
 
 
@@ -793,6 +795,7 @@ void CS_Delete(T_Cluster_set * cs)
 		cs->clusters = nxt;
 	}
 	free(cs);
+  cs = NULL;
 }
 
 
@@ -1019,7 +1022,7 @@ T_Gradient_set * GS_New(T_Cluster_set * cs)
     n=(T_Gradient_set *)malloc(sizeof(T_Gradient_set));
     if (n!=NULL)
     {
-        // On recopie les paramŠtres demand‚s
+        // On recopie les paramètres demandés
         n->nb_max=cs->nb_max;
 
         // On tente d'allouer la table
@@ -1029,9 +1032,9 @@ T_Gradient_set * GS_New(T_Cluster_set * cs)
             GS_Init(n,cs);
         else
         {
-            // Table impossible … allouer
+            // Table impossible à allouer
             free(n);
-            n=0;
+            n=NULL;
         }
     }
 
diff --git a/operatio.c b/operatio.c
index d528a2c1..6d8e1711 100644
--- a/operatio.c
+++ b/operatio.c
@@ -2226,6 +2226,7 @@ void Polyfill_12_9(void)
     Display_all_screen();
     Polyfill(Polyfill_number_of_points,Polyfill_table_of_points,color);
     free(Polyfill_table_of_points);
+    Polyfill_table_of_points = NULL;
 
     End_of_modification();
     if ( (Config.Coords_rel) && (Menu_is_visible) )
@@ -2556,6 +2557,7 @@ void Filled_polyform_12_8(void)
     Display_all_screen();
     Polyfill(Polyfill_number_of_points,Polyfill_table_of_points,color);
     free(Polyfill_table_of_points);
+    Polyfill_table_of_points = NULL;
 
     Paintbrush_hidden=0;
 
@@ -2640,6 +2642,7 @@ void Filled_contour_0_8(void)
   Display_all_screen();
   Polyfill(Polyfill_number_of_points,Polyfill_table_of_points,color);
   free(Polyfill_table_of_points);
+  Polyfill_table_of_points = NULL;
 
   Paintbrush_hidden=0;
 
diff --git a/pages.c b/pages.c
index a55e77fb..8b732984 100644
--- a/pages.c
+++ b/pages.c
@@ -116,8 +116,9 @@ void Free_layer(T_Page * page, byte layer)
   ptr = (short *)(page->Image[layer]);
   if (-- (*(ptr-1))) // Users--
     return;
-  else
+  else {
     free(ptr-1);
+  }
     
   // Stats
   Stats_pages_number--;
@@ -486,6 +487,7 @@ void Free_last_page_of_list(T_List_of_pages * list)
         page->Prev->Next = page->Next;
         Clear_page(page);
         free(page);
+        page = NULL;
         list->List_size--;
     }
   }
diff --git a/palette.c b/palette.c
index 73a156b7..1ea2ccc7 100644
--- a/palette.c
+++ b/palette.c
@@ -2209,6 +2209,7 @@ void Button_Palette(void)
   free(backup_palette);
   free(temp_palette);
   free(working_palette);
+  backup_palette = temp_palette = working_palette = NULL;
 }