diff --git a/stackit/internal/services/postgresflex/instance/resource.go b/stackit/internal/services/postgresflex/instance/resource.go
index 82119366..276374fe 100644
--- a/stackit/internal/services/postgresflex/instance/resource.go
+++ b/stackit/internal/services/postgresflex/instance/resource.go
@@ -224,6 +224,9 @@ func (r *instanceResource) Schema(_ context.Context, _ resource.SchemaRequest, r
 				Attributes: map[string]schema.Attribute{
 					"class": schema.StringAttribute{
 						Required: true,
+						PlanModifiers: []planmodifier.String{
+							stringplanmodifier.RequiresReplace(),
+						},
 					},
 					"size": schema.Int64Attribute{
 						Required: true,