diff --git a/plugins/market b/plugins/market
index 0078a98..3c4a0b8 100644
--- a/plugins/market
+++ b/plugins/market
@@ -37,10 +37,26 @@ sub command :Tab(market,&tab) {
     my $space    = parse_amount($product->{ space })  or return NEXT;
     my $description = $product->{description};
 
-    $cart
-        ->add(-($seller + $space), "$description (sold by $username)", {product_id=>$command})
-        ->add_contra($username, 0+$seller, "\$you bought $description")
-        if 0+$seller;
+    my @existing = grep {
+        $_->attribute('plugin') eq $self->id and
+        $_->attribute('product_id') eq $command
+    } $cart->entries('plugin');
+
+    if (@existing) {
+        $existing[0]->quantity($existing[0]->quantity + 1);
+        return ACCEPT;
+    }
+
+    $cart->add(
+        -($seller + $space),
+        "$description (sold by $username)",
+        { product_id => $command, plugin => $self->id }
+    )->add_contra(
+        $username,
+        $seller,
+        "\$you bought $description"
+    );
+
     return ACCEPT;
 }
 
diff --git a/plugins/products b/plugins/products
index ba8c10c..bee1599 100644
--- a/plugins/products
+++ b/plugins/products
@@ -34,10 +34,20 @@ sub command :Tab(edit,&tab) {
 
     my $price = parse_amount( $product->{price} ) or return NEXT;
 
+    my @existing = grep {
+        $_->attribute('plugin') eq $self->id and
+        $_->attribute('product_id') eq $product->{id}
+    } $cart->entries('plugin');
+
+    if (@existing) {
+        $existing[0]->quantity($existing[0]->quantity + 1);
+        return ACCEPT;
+    }
+
     $cart->add(
         -$price,
         $product->{description},
-        { product_id => $product->{id} }
+        { product_id => $product->{id}, plugin => $self->id }
     );
     return ACCEPT;
 }