diff --git a/InvenTree/part/migrations/0073_auto_20211013_1048.py b/InvenTree/part/migrations/0073_auto_20211013_1048.py
new file mode 100644
index 0000000000..e581af603e
--- /dev/null
+++ b/InvenTree/part/migrations/0073_auto_20211013_1048.py
@@ -0,0 +1,21 @@
+# Generated by Django 3.2.5 on 2021-10-13 10:48
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('part', '0072_bomitemsubstitute'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='bomitemsubstitute',
+            options={'verbose_name': 'BOM Item Substitute'},
+        ),
+        migrations.AlterUniqueTogether(
+            name='bomitemsubstitute',
+            unique_together={('part', 'bom_item')},
+        ),
+    ]
diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index 0be1f5fc31..85dd9042fc 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -2623,6 +2623,26 @@ class BomItemSubstitute(models.Model):
         part: The part which can be used as a substitute
     """
 
+    class Meta:
+        verbose_name = _("BOM Item Substitute")
+
+        # Prevent duplication of substitute parts
+        unique_together = ('part', 'bom_item')
+
+    def validate_unique(self, exclude=None):
+        """
+        Ensure that this BomItemSubstitute is "unique":
+
+        - It cannot point to the same "part" as the "sub_part" of the parent "bom_item"
+        """
+
+        super().validate_unique(exclude=exclude)
+
+        if self.part == self.bom_item.sub_part:
+            raise ValidationError({
+                "part": _("Substitute part cannot be the same as the master part"),
+            })
+
     @staticmethod
     def get_api_url():
         return reverse('api-bom-substitute-list')
diff --git a/InvenTree/templates/js/translated/bom.js b/InvenTree/templates/js/translated/bom.js
index a5e1153bad..19426ba1d2 100644
--- a/InvenTree/templates/js/translated/bom.js
+++ b/InvenTree/templates/js/translated/bom.js
@@ -213,11 +213,16 @@ function bomSubstitutesDialog(bom_item_id, substitutes, options={}) {
     constructForm('{% url "api-bom-substitute-list" %}', {
         method: 'POST',
         fields: {
+            bom_item: {
+                hidden: true,
+                value: bom_item_id,
+            },
             part: {
                 required: false,
             },
         },
         preFormContent: html,
+        cancelText: '{% trans "Close" %}',
         submitText: '{% trans "Add Substitute" %}',
         title: '{% trans "Edit BOM Item Substitutes" %}',
         afterRender: function(fields, opts) {
@@ -243,8 +248,22 @@ function bomSubstitutesDialog(bom_item_id, substitutes, options={}) {
                 });
             });
         },
-        onSubmit: function(fields, opts) {
-            // TODO
+        preventClose: true,
+        onSuccess: function(response, opts) {
+
+            // Clear the form
+            var field = {
+                type: 'related field',
+            };
+
+            updateFieldValue('part', null, field, opts);
+
+            // Add the new substitute to the table
+            var row = renderSubstituteRow(response);
+            $(opts.modal).find('#substitute-table > tbody:last-child').append(row);
+
+            // Re-enable the "submit" button
+            $(opts.modal).find('#modal-form-submit').prop('disabled', false);
         }
     });