diff --git a/types/n3/index.d.ts b/types/n3/index.d.ts
index 31a2975bb0..75a8c4efef 100644
--- a/types/n3/index.d.ts
+++ b/types/n3/index.d.ts
@@ -3,7 +3,7 @@
 // Definitions by: Fred Eisele <https://github.com/phreed>
 //                 Ruben Taelman <https://github.com/rubensworks>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
-// TypeScript Version: 2.1
+// TypeScript Version: 2.3
 
 /// <reference types="node" />
 
@@ -12,10 +12,12 @@ import * as stream from "stream";
 import * as RDF from "rdf-js";
 import { EventEmitter } from "events";
 
-export interface Prefixes {
-    [key: string]: RDF.NamedNode;
+export interface Prefixes<I = RDF.NamedNode> {
+  [key: string]: I;
 }
 
+export type PrefixedToIri = (suffix: string) => RDF.NamedNode;
+
 export class Term implements RDF.Term {
     termType: "NamedNode" | "BlankNode" | "Literal" | "Variable" | "DefaultGraph";
     id: string;
@@ -139,7 +141,7 @@ export interface N3StreamParser extends RDF.Stream, NodeJS.WritableStream, RDF.S
 
 export interface WriterOptions {
     format?: string;
-    prefixes?: Prefixes;
+    prefixes?: Prefixes<RDF.NamedNode | string>;
     end?: boolean;
 }
 
@@ -157,8 +159,8 @@ export interface N3Writer {
     addQuad(subject: RDF.Term, predicate: RDF.Term, object: RDF.Term | RDF.Term[], graph?: RDF.Term, done?: () => void): void;
     addQuad(quad: RDF.Quad): void;
     addQuads(quads: RDF.Quad[]): void;
-    addPrefix(prefix: string, iri: string, done?: () => void): void;
-    addPrefixes(prefixes: Prefixes, done?: () => void): void;
+    addPrefix(prefix: string, iri: RDF.NamedNode | string , done?: () => void): void;
+    addPrefixes(prefixes: Prefixes<RDF.NamedNode | string>, done?: () => void): void;
     end(err?: ErrorCallback, result?: string): void;
     blank(predicate: RDF.Term, object: RDF.Term): RDF.Term;
     blank(triple: BlankTriple | RDF.Quad | BlankTriple[] | RDF.Quad[]): RDF.Term;
@@ -218,6 +220,9 @@ export namespace Util {
     function isVariable(value: RDF.Term | null): boolean;
     function isDefaultGraph(value: RDF.Term | null): boolean;
     function inDefaultGraph(value: RDF.Quad): boolean;
-    function prefix(iri: string, factory?: RDF.DataFactory): (suffix: string) => RDF.NamedNode;
-    function prefixes(defaultPrefixes: Prefixes, factory?: RDF.DataFactory): (iri: string) => (suffix: string) => RDF.NamedNode;
+    function prefix(iri: RDF.NamedNode|string, factory?: RDF.DataFactory): PrefixedToIri;
+    function prefixes(
+      defaultPrefixes: Prefixes<RDF.NamedNode|string>,
+      factory?: RDF.DataFactory
+    ): (prefix: string) => PrefixedToIri;
 }
diff --git a/types/n3/n3-tests.ts b/types/n3/n3-tests.ts
index a061777ad7..f7b2db2409 100644
--- a/types/n3/n3-tests.ts
+++ b/types/n3/n3-tests.ts
@@ -17,7 +17,8 @@ function test_add_prefixes() {
 
     writer.addPrefixes({
         freebase: N3.DataFactory.namedNode("http://rdf.freebase.com/ns/"),
-        xsd: N3.DataFactory.namedNode("http://www.w3.org/2001/XMLSchema#")
+        xsd: N3.DataFactory.namedNode("http://www.w3.org/2001/XMLSchema#"),
+        rdf: 'http://test'
     });
 
     writer.end((error, result) => {
@@ -31,7 +32,7 @@ function test_serialize() {
             format: "ttl",
             prefixes: {
                 foaf: "http://xmlns.com/foaf/0.1",
-                freebase: "http://rdf.freebase.com/ns/",
+                freebase: N3.DataFactory.namedNode("http://rdf.freebase.com/ns/"),
                 g: "http://base.google.com/ns/1.0"
             }
         });