diff --git a/pkg/apis/identity/assignments.go b/pkg/apis/identity/assignments.go
index f2c61aa5ee..cd3afa6551 100644
--- a/pkg/apis/identity/assignments.go
+++ b/pkg/apis/identity/assignments.go
@@ -86,7 +86,8 @@ type RoleAssignmentsInput struct {
 	Projects []string `json:"projects"`
 	Domains  []string `json:"domains"`
 
-	ProjectDomains []string `json:"project_domains"`
+	ProjectDomainId string   `json:"project_domain_id"`
+	ProjectDomains  []string `json:"project_domains"`
 
 	IncludeNames    *bool `json:"include_names"`
 	Effective       *bool `json:"effective"`
diff --git a/pkg/keystone/models/assignments.go b/pkg/keystone/models/assignments.go
index 28ee8842d4..3c99a1b84e 100644
--- a/pkg/keystone/models/assignments.go
+++ b/pkg/keystone/models/assignments.go
@@ -458,7 +458,7 @@ func roleAssignmentHandler(ctx context.Context, w http.ResponseWriter, r *http.R
 		input.Role.Id,
 		input.Scope.Domain.Id,
 		input.Scope.Project.Id,
-		"",
+		input.ProjectDomainId,
 		input.Users,
 		input.Groups,
 		input.Roles,