diff --git a/docs/docs/index.md b/docs/docs/index.md
index 6335357..a33fa78 100644
--- a/docs/docs/index.md
+++ b/docs/docs/index.md
@@ -65,7 +65,8 @@ job function.
     and marked as `failed`. Its default unit is second and it can be an integer or a string representing an integer(e.g.  `2`, `'2'`). Furthermore, it can be a string with specify unit including hour, minute, second(e.g. `'1h'`, `'3m'`, `'5s'`).
 * `result_ttl` specifies the expiry time of the key where the job result will
   be stored
-* `ttl` specifies the maximum queued time of the job before it'll be cancelled
+* `ttl` specifies the maximum queued time of the job before it'll be cancelled. 
+  If you specify a value of `-1` you indicate an infinite job ttl and it will run indefinitely
 * `depends_on` specifies another job (or job id) that must complete before this
   job will be queued
 * `job_id` allows you to manually specify this job's `job_id`
diff --git a/rq/registry.py b/rq/registry.py
index 74039fd..2b8b992 100644
--- a/rq/registry.py
+++ b/rq/registry.py
@@ -39,8 +39,10 @@ class BaseRegistry(object):
         return self.connection.zcard(self.key)
 
     def add(self, job, ttl=0, pipeline=None):
-        """Adds a job to a registry with expiry time of now + ttl."""
+        """Adds a job to a registry with expiry time of now + ttl, unless it's -1 which is set to +inf"""
         score = ttl if ttl < 0 else current_timestamp() + ttl
+        if score == -1:
+            score = '+inf'
         if pipeline is not None:
             return pipeline.zadd(self.key, score, job.id)
 
diff --git a/tests/test_registry.py b/tests/test_registry.py
index 295d284..41d0c1c 100644
--- a/tests/test_registry.py
+++ b/tests/test_registry.py
@@ -51,9 +51,9 @@ class TestRegistry(RQTestCase):
         self.assertLess(self.testconn.zscore(self.registry.key, job.id),
                         timestamp + 1002)
 
-        # Ensure that a timeout of -1 results in a score of -1
+        # Ensure that a timeout of -1 results in a score of inf
         self.registry.add(job, -1)
-        self.assertEqual(self.testconn.zscore(self.registry.key, job.id), -1)
+        self.assertEqual(self.testconn.zscore(self.registry.key, job.id), float('inf'))
 
         # Ensure that job is properly removed from sorted set
         self.registry.remove(job)