diff --git a/src/N3Writer.js b/src/N3Writer.js
index 243a088b..6eb16a33 100644
--- a/src/N3Writer.js
+++ b/src/N3Writer.js
@@ -297,7 +297,7 @@ export default class N3Writer {
       }
       IRIlist = escapeRegex(IRIlist, /[\]\/\(\)\*\+\?\.\\\$]/g, '\\$&');
       this._prefixRegex = new RegExp(`^(?:${prefixList})[^\/]*$|` +
-                                     `^(${IRIlist})([_a-zA-Z][\\-_a-zA-Z0-9]*)$`);
+                                     `^(${IRIlist})([_a-zA-Z0-9][\\-_a-zA-Z0-9]*)$`);
     }
     // End a prefix block with a newline
     this._write(hasPrefixes ? '\n' : '', done);
diff --git a/test/N3StreamWriter-test.js b/test/N3StreamWriter-test.js
index 4b8d35b9..0e02629b 100644
--- a/test/N3StreamWriter-test.js
+++ b/test/N3StreamWriter-test.js
@@ -41,7 +41,7 @@ describe('StreamWriter', () => {
                       '@prefix c: <http://a.org/b>.\n\n' +
                       'a:bc b:ef a:bhi.\n' +
                       '<http://a.org/bc/de> <http://a.org/b#e#f> <http://a.org/b#x/t>.\n' +
-                      '<http://a.org/3a> <http://a.org/b#3a> b:a3.\n'),
+                      'a:3a b:3a b:a3.\n'),
     );
 
     it('should take over prefixes from the input stream', done => {
diff --git a/test/N3Writer-test.js b/test/N3Writer-test.js
index c44ff280..78e17bbc 100644
--- a/test/N3Writer-test.js
+++ b/test/N3Writer-test.js
@@ -271,7 +271,7 @@ describe('Writer', () => {
                       '@prefix c: <http://a.org/b>.\n\n' +
                       'a:bc b:ef a:bhi.\n' +
                       '<http://a.org/bc/de> <http://a.org/b#e#f> <http://a.org/b#x/t>.\n' +
-                      '<http://a.org/3a> <http://a.org/b#3a> b:a3.\n'),
+                      'a:3a b:3a b:a3.\n'),
     );
 
     it(
@@ -902,6 +902,7 @@ describe('Writer', () => {
         writer.quadToString(new NamedNode('a'), new NamedNode('b'), new Quad(new NamedNode('a'), new NamedNode('b'), new NamedNode('c'), new NamedNode('g'))),
       ).toBe('<a> <b> <<<a> <b> <c> <g>>> .\n');
     });
+
   });
 });