diff --git a/BrickOwlSharp.Client/BrickOwlClient.cs b/BrickOwlSharp.Client/BrickOwlClient.cs
index 4c85d9c..7f34777 100644
--- a/BrickOwlSharp.Client/BrickOwlClient.cs
+++ b/BrickOwlSharp.Client/BrickOwlClient.cs
@@ -249,7 +249,12 @@ public async Task<List<Inventory>> GetInventoryAsync(
             var url = new Uri(_baseUri, $"inventory/list").ToString();
 
             url = AppendOptionalParam(url, "filter", filter);
-            url = AppendOptionalParam(url, "active_only", activeOnly);
+
+            if (activeOnly.HasValue)
+            {               
+                url = AppendOptionalParam(url, "active_only", activeOnly.Value == true ? 1 : 0);
+            }
+
             url = AppendOptionalParam(url, "external_id_1", externalId);
             url = AppendOptionalParam(url, "lot_id", lotId);