diff --git a/demos/constraint-editor/constraint-editor-window.c b/demos/constraint-editor/constraint-editor-window.c
index ba25a806ec..ca18e27cf8 100644
--- a/demos/constraint-editor/constraint-editor-window.c
+++ b/demos/constraint-editor/constraint-editor-window.c
@@ -36,7 +36,7 @@ struct _ConstraintEditorWindow
 G_DEFINE_TYPE(ConstraintEditorWindow, constraint_editor_window, GTK_TYPE_APPLICATION_WINDOW);
 
 static GtkConstraintTarget *
-find_target (GListModel *model,
+find_target (GListModel          *model,
              GtkConstraintTarget *orig)
 {
   const char *name;
@@ -163,20 +163,30 @@ constraint_editor_window_load (ConstraintEditorWindow *self,
       GtkConstraint *clone;
       GtkConstraintTarget *target;
       GtkConstraintTarget *source;
+      GtkConstraintAttribute source_attr;
 
       item = g_list_model_get_item (list, i);
       constraint = GTK_CONSTRAINT (item);
 
       target = gtk_constraint_get_target (constraint);
       source = gtk_constraint_get_source (constraint);
-      clone = gtk_constraint_new (find_target (constraint_view_get_model (CONSTRAINT_VIEW (self->view)), target),
+      source_attr = gtk_constraint_get_source_attribute (constraint);
+
+      if (source == NULL && source_attr == GTK_CONSTRAINT_ATTRIBUTE_NONE)
+        clone = gtk_constraint_new_constant (find_target (constraint_view_get_model (CONSTRAINT_VIEW (self->view)), target),
                                   gtk_constraint_get_target_attribute (constraint),
                                   gtk_constraint_get_relation (constraint),
-                                  find_target (constraint_view_get_model (CONSTRAINT_VIEW (self->view)), source),
-                                  gtk_constraint_get_target_attribute (constraint),
-                                  gtk_constraint_get_multiplier (constraint),
                                   gtk_constraint_get_constant (constraint),
                                   gtk_constraint_get_strength (constraint));
+      else
+        clone = gtk_constraint_new (find_target (constraint_view_get_model (CONSTRAINT_VIEW (self->view)), target),
+                                    gtk_constraint_get_target_attribute (constraint),
+                                    gtk_constraint_get_relation (constraint),
+                                    find_target (constraint_view_get_model (CONSTRAINT_VIEW (self->view)), source),
+                                    source_attr,
+                                    gtk_constraint_get_multiplier (constraint),
+                                    gtk_constraint_get_constant (constraint),
+                                    gtk_constraint_get_strength (constraint));
 
       constraint_view_add_constraint (CONSTRAINT_VIEW (self->view), clone);
 
@@ -300,7 +310,7 @@ save_response_cb (GtkNativeDialog        *dialog,
       model = constraint_view_get_model (CONSTRAINT_VIEW (self->view));
       text = serialize_model (model);
       file = gtk_file_chooser_get_file (GTK_FILE_CHOOSER (dialog));
-      g_file_replace_contents (file, text, -1,
+      g_file_replace_contents (file, text, strlen (text),
                                NULL, FALSE,
                                G_FILE_CREATE_NONE,
                                NULL,
diff --git a/demos/constraint-editor/constraint-editor.c b/demos/constraint-editor/constraint-editor.c
index 62af6e356f..6f897b2d8a 100644
--- a/demos/constraint-editor/constraint-editor.c
+++ b/demos/constraint-editor/constraint-editor.c
@@ -142,6 +142,9 @@ get_target (GListModel *model,
 {
   int i;
 
+  if (id == NULL)
+    return NULL;
+
   if (strcmp ("super", id) == 0)
     return NULL;
 
@@ -212,6 +215,22 @@ get_relation_nick (GtkConstraintRelation relation)
   return nick;
 }
 
+static const char *
+get_relation_display_name (GtkConstraintRelation relation)
+{
+  switch (relation)
+    {
+    case GTK_CONSTRAINT_RELATION_LE:
+      return "≤";
+    case GTK_CONSTRAINT_RELATION_EQ:
+      return "=";
+    case GTK_CONSTRAINT_RELATION_GE:
+      return "≥";
+    default:
+      return "?";
+    }
+}
+
 static GtkConstraintStrength
 get_strength (const char *id)
 {
@@ -331,6 +350,7 @@ source_attr_changed (ConstraintEditor *editor)
     {
       gtk_widget_set_sensitive (editor->source, TRUE);
       gtk_widget_set_sensitive (editor->multiplier, TRUE);
+      gtk_editable_set_text (GTK_EDITABLE (editor->multiplier), "1");
     }
 }
 
@@ -347,7 +367,7 @@ constraint_editor_constraint_to_string (GtkConstraint *constraint)
 
   name = get_target_name (gtk_constraint_get_target (constraint));
   attr = get_attr_nick (gtk_constraint_get_target_attribute (constraint));
-  relation = get_relation_nick (gtk_constraint_get_relation (constraint));
+  relation = get_relation_display_name (gtk_constraint_get_relation (constraint));
 
   if (name == NULL)
     name = "[ ]";
@@ -441,8 +461,12 @@ update_preview (ConstraintEditor *editor)
 static void
 update_button (ConstraintEditor *editor)
 {
-  if (gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->target)) != NULL &&
-      gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source)) != NULL)
+  const char *target = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->target));
+  const char *source = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source));
+  const char *source_attr = gtk_combo_box_get_active_id (GTK_COMBO_BOX (editor->source_attr));
+
+  if (target &&
+      (source || (source_attr && get_target_attr (source_attr) == GTK_CONSTRAINT_ATTRIBUTE_NONE)))
     gtk_widget_set_sensitive (editor->button, TRUE);
   else
     gtk_widget_set_sensitive (editor->button, FALSE);
diff --git a/demos/constraint-editor/constraint-editor.ui b/demos/constraint-editor/constraint-editor.ui
index d7c0d0e25b..d201aae350 100644
--- a/demos/constraint-editor/constraint-editor.ui
+++ b/demos/constraint-editor/constraint-editor.ui
@@ -78,6 +78,7 @@
           <object class="GtkComboBoxText" id="source_attr">
             <signal name="changed" handler="update_preview" swapped="yes"/>
             <signal name="changed" handler="source_attr_changed" swapped="yes"/>
+            <signal name="changed" handler="update_button" swapped="yes"/>
             <layout>
               <property name="column">2</property>
               <property name="row">3</property>
diff --git a/gtk/gtkconstraintlayout.c b/gtk/gtkconstraintlayout.c
index e5d6037962..92fbfcc416 100644
--- a/gtk/gtkconstraintlayout.c
+++ b/gtk/gtkconstraintlayout.c
@@ -1431,18 +1431,18 @@ constraint_data_to_constraint (const ConstraintData *data,
   else
     strength = GTK_CONSTRAINT_STRENGTH_REQUIRED;
 
-  if (source != NULL && source_attr != GTK_CONSTRAINT_ATTRIBUTE_NONE)
+  if (source == NULL && source_attr == GTK_CONSTRAINT_ATTRIBUTE_NONE)
+    return gtk_constraint_new_constant (target, target_attr,
+                                        relation,
+                                        data->constant,
+                                        strength);
+  else
     return gtk_constraint_new (target, target_attr,
                                relation,
                                source, source_attr,
                                data->multiplier,
                                data->constant,
                                strength);
-
-  return gtk_constraint_new_constant (target, target_attr,
-                                      relation,
-                                      data->constant,
-                                      strength);
 }
 
 static GtkConstraintGuide *