diff --git a/libs/gtkmm2ext/gtkmm2ext/keyboard.h b/libs/gtkmm2ext/gtkmm2ext/keyboard.h
index 21df853e89..09d549cd32 100644
--- a/libs/gtkmm2ext/gtkmm2ext/keyboard.h
+++ b/libs/gtkmm2ext/gtkmm2ext/keyboard.h
@@ -60,10 +60,11 @@ public:
 	typedef std::vector<uint32_t> State;
 	typedef uint32_t              ModifierMask;
 
-	static uint32_t PrimaryModifier;
-	static uint32_t SecondaryModifier;
-	static uint32_t TertiaryModifier;
-	static uint32_t Level4Modifier;
+	static const uint32_t PrimaryModifier;
+	static const uint32_t SecondaryModifier;
+	static const uint32_t TertiaryModifier;
+	static const uint32_t Level4Modifier;
+
 	static uint32_t CopyModifier;
 	static uint32_t RangeSelectModifier;
 	static uint32_t GainFineScaleModifier;
@@ -88,30 +89,6 @@ public:
 	static const char* tertiary_modifier_short_name ();
 	static const char* level4_modifier_short_name ();
 
-	static void set_primary_modifier (uint32_t newval)
-	{
-		set_modifier (newval, PrimaryModifier);
-	}
-	static void set_secondary_modifier (uint32_t newval)
-	{
-		set_modifier (newval, SecondaryModifier);
-	}
-	static void set_tertiary_modifier (uint32_t newval)
-	{
-		set_modifier (newval, TertiaryModifier);
-	}
-	static void set_level4_modifier (uint32_t newval)
-	{
-		set_modifier (newval, Level4Modifier);
-	}
-	static void set_copy_modifier (uint32_t newval)
-	{
-		set_modifier (newval, CopyModifier);
-	}
-	static void set_range_select_modifier (uint32_t newval)
-	{
-		set_modifier (newval, RangeSelectModifier);
-	}
 
 	bool  key_is_down (uint32_t keyval);
 	guint modifier_state ();
@@ -138,6 +115,15 @@ public:
 
 	static bool no_modifiers_active (guint state);
 
+	static void set_copy_modifier (uint32_t newval)
+	{
+		set_modifier (newval, CopyModifier);
+	}
+	static void set_range_select_modifier (uint32_t newval)
+	{
+		set_modifier (newval, RangeSelectModifier);
+	}
+
 	static void set_snap_modifier (guint);
 	static void set_snap_delta_modifier (guint);
 	static void set_edit_button (guint);
diff --git a/libs/gtkmm2ext/keyboard.cc b/libs/gtkmm2ext/keyboard.cc
index b17814c81e..7a0fd97a5b 100644
--- a/libs/gtkmm2ext/keyboard.cc
+++ b/libs/gtkmm2ext/keyboard.cc
@@ -64,10 +64,11 @@ guint Keyboard::insert_note_mod = GDK_CONTROL_MASK;
 
 #ifdef __APPLE__
 
-guint Keyboard::PrimaryModifier          = GDK_MOD2_MASK;    // Command
-guint Keyboard::SecondaryModifier        = GDK_CONTROL_MASK; // Control
-guint Keyboard::TertiaryModifier         = GDK_SHIFT_MASK;   // Shift
-guint Keyboard::Level4Modifier           = GDK_MOD1_MASK;    // Alt/Option
+guint const Keyboard::PrimaryModifier   = GDK_MOD2_MASK;    // Command
+guint const Keyboard::SecondaryModifier = GDK_CONTROL_MASK; // Control
+guint const Keyboard::TertiaryModifier  = GDK_SHIFT_MASK;   // Shift
+guint const Keyboard::Level4Modifier    = GDK_MOD1_MASK;    // Alt/Option
+
 guint Keyboard::CopyModifier             = GDK_CONTROL_MASK; // Control
 guint Keyboard::RangeSelectModifier      = GDK_SHIFT_MASK;
 guint Keyboard::button2_modifiers        = Keyboard::SecondaryModifier | Keyboard::Level4Modifier;
@@ -129,10 +130,11 @@ guint Keyboard::snap_delta_mod = Keyboard::Level4Modifier;
 
 #else
 
-guint Keyboard::PrimaryModifier          = GDK_CONTROL_MASK;               // Control
-guint Keyboard::SecondaryModifier        = GDK_MOD1_MASK;                  // Alt/Option
-guint Keyboard::TertiaryModifier         = GDK_SHIFT_MASK;                 // Shift
-guint Keyboard::Level4Modifier           = GDK_MOD4_MASK | GDK_SUPER_MASK; // Mod4/Windows
+guint const Keyboard::PrimaryModifier   = GDK_CONTROL_MASK;               // Control
+guint const Keyboard::SecondaryModifier = GDK_MOD1_MASK;                  // Alt/Option
+guint const Keyboard::TertiaryModifier  = GDK_SHIFT_MASK;                 // Shift
+guint const Keyboard::Level4Modifier    = GDK_MOD4_MASK | GDK_SUPER_MASK; // Mod4/Windows
+
 guint Keyboard::CopyModifier             = GDK_CONTROL_MASK;
 guint Keyboard::RangeSelectModifier      = GDK_SHIFT_MASK;
 guint Keyboard::button2_modifiers        = 0; /* not used */