diff --git a/src/buttons.c b/src/buttons.c
index 83223b42..d334b8d9 100644
--- a/src/buttons.c
+++ b/src/buttons.c
@@ -4901,7 +4901,7 @@ void Button_Effects(int btn)
 
 
       case 14: // Constraint checker/enforcer
-        if (Window_attribute1==LEFT_SIDE)
+        if (Window_attribute1==LEFT_SIDE && Selected_Constraint_Mode > IMAGE_MODE_ANIMATION)
         {
           Button_Constraint_mode();
           Hide_cursor();
diff --git a/src/buttons_effects.c b/src/buttons_effects.c
index 072ec8d8..c9e09e21 100644
--- a/src/buttons_effects.c
+++ b/src/buttons_effects.c
@@ -163,7 +163,6 @@ void Menu_tag_colors(char * window_title, byte * table, byte * mode, byte can_ca
   Display_cursor();
 }
 
-static enum IMAGE_MODES Selected_Constraint_Mode = 0;
 
 /// Constaint enforcer/checker
 ///
diff --git a/src/global.h b/src/global.h
index 3e36627a..5576f935 100644
--- a/src/global.h
+++ b/src/global.h
@@ -561,6 +561,12 @@ GFX2_GLOBAL byte Mask_mode;
 /// Array of booleans. True if the indexed color is protected by the mask.
 GFX2_GLOBAL byte Mask_table[256];
 
+// -- 8 bit constraints mode
+
+/// Selected constraint mode
+GFX2_GLOBAL enum IMAGE_MODES Selected_Constraint_Mode;
+
+
 // -- Magnifier data
 
 #ifdef GLOBAL_VARIABLES
diff --git a/src/helpfile.h b/src/helpfile.h
index 9869abc5..18b614d4 100644
--- a/src/helpfile.h
+++ b/src/helpfile.h
@@ -1926,11 +1926,20 @@ static const T_Help_table helptable_effects[] =
   HELP_TEXT ("8bits computers video modes, such as the ZX")
   HELP_TEXT ("Spectrum, Commodore 64, etc.")
   HELP_BOLD ("LEFT CLICK")
-  HELP_TEXT ("Enable/disable the contraints")
+  HELP_TEXT ("Open the menu if no constraint type has been")
+  HELP_TEXT ("already selected.")
+  HELP_TEXT ("Else enable/disable the contraints")
   HELP_TEXT ("")
   HELP_BOLD ("RIGHT CLICK")
-  HELP_TEXT ("Opens the menu to choose the type of")
-  HELP_TEXT ("constraints")
+  HELP_TEXT ("Open the menu to choose the type of")
+  HELP_TEXT ("constraints.")
+  HELP_TEXT ("")
+  HELP_TEXT ("")
+  HELP_BOLD ("Block modes")
+  HELP_TEXT ("ZX Spectrum, Thomson MOTO, C64 multicolor,")
+  HELP_TEXT ("C64 HiRes are modes with block constraints.")
+  HELP_TEXT ("Only a limited different colors (generaly 2)")
+  HELP_TEXT ("are allowed in a pixel block.")
   HELP_TEXT ("")
   HELP_TEXT ("")
   HELP_BOLD ("Amstrad CPC Mode5")