diff --git a/public/viewjs/productform.js b/public/viewjs/productform.js
index 6292a7a6..3761b2f5 100644
--- a/public/viewjs/productform.js
+++ b/public/viewjs/productform.js
@@ -186,6 +186,20 @@
 	}
 });
 
+Grocy.Api.Get('stock/products/' + Grocy.EditObjectId,
+	function(productDetails)
+	{
+		if (productDetails.last_purchased == null)
+		{
+			$('#qu_id_stock').removeAttr("disabled");
+		}
+	},
+	function(xhr)
+	{
+		console.error(xhr);
+	}
+);
+
 var prefillName = GetUriParam('prefillname');
 if (prefillName !== undefined)
 {
diff --git a/views/productform.blade.php b/views/productform.blade.php
index 10eb367d..09a6c2b1 100644
--- a/views/productform.blade.php
+++ b/views/productform.blade.php
@@ -170,7 +170,8 @@
 
 			<div class="form-group">
 				<label for="qu_id_stock">{{ $__t('Quantity unit stock') }}</label>
-				<select required class="form-control input-group-qu" id="qu_id_stock" name="qu_id_stock">
+				<i class="fas fa-question-circle" data-toggle="tooltip" title="Quantity unit stock cannot be changed after first purchase"></i>
+				<select required class="form-control input-group-qu" id="qu_id_stock" name="qu_id_stock" @if($mode == 'edit') disabled @endif>
 					<option></option>
 					@foreach($quantityunits as $quantityunit)
 						<option @if($mode == 'edit' && $quantityunit->id == $product->qu_id_stock) selected="selected" @endif value="{{ $quantityunit->id }}" data-plural-form="{{ $quantityunit->name_plural }}">{{ $quantityunit->name }}</option>