diff --git a/python/ray/includes/unique_ids.pxi b/python/ray/includes/unique_ids.pxi
index edb280e68..872571b42 100644
--- a/python/ray/includes/unique_ids.pxi
+++ b/python/ray/includes/unique_ids.pxi
@@ -288,6 +288,7 @@ cdef class JobID(BaseID):
 
     @classmethod
     def from_int(cls, value):
+        assert value < 65536, "Maximum JobID integer is 65535."
         return cls(CJobID.FromInt(value).Binary())
 
     @classmethod
diff --git a/python/ray/worker.py b/python/ray/worker.py
index 80d4844f0..79942fb3f 100644
--- a/python/ray/worker.py
+++ b/python/ray/worker.py
@@ -1111,9 +1111,8 @@ def connect(node,
         if setproctitle:
             setproctitle.setproctitle("ray::IDLE")
     elif mode is LOCAL_MODE:
-        # Code path of local mode
         if job_id is None:
-            job_id = JobID.from_int(random.randint(1, 100000))
+            job_id = JobID.from_int(random.randint(1, 65535))
         worker.worker_id = ray.utils.compute_driver_id_from_job(
             job_id).binary()
     else:
diff --git a/src/ray/common/id.cc b/src/ray/common/id.cc
index da819e191..cf3b9d678 100644
--- a/src/ray/common/id.cc
+++ b/src/ray/common/id.cc
@@ -360,7 +360,7 @@ ObjectID ObjectID::GenerateObjectId(const std::string &task_id_binary,
   return ret;
 }
 
-JobID JobID::FromInt(uint32_t value) {
+JobID JobID::FromInt(uint16_t value) {
   std::vector<uint8_t> data(JobID::Size(), 0);
   std::memcpy(data.data(), &value, JobID::Size());
   return JobID::FromBinary(
diff --git a/src/ray/common/id.h b/src/ray/common/id.h
index b95b88fd5..8005e2971 100644
--- a/src/ray/common/id.h
+++ b/src/ray/common/id.h
@@ -99,9 +99,9 @@ class UniqueID : public BaseID<UniqueID> {
 
 class JobID : public BaseID<JobID> {
  public:
-  static constexpr int64_t kLength = 4;
+  static constexpr int64_t kLength = 2;
 
-  static JobID FromInt(uint32_t value);
+  static JobID FromInt(uint16_t value);
 
   static size_t Size() { return kLength; }
 
@@ -161,7 +161,7 @@ class ActorID : public BaseID<ActorID> {
 
 class TaskID : public BaseID<TaskID> {
  private:
-  static constexpr size_t kUniqueBytesLength = 6;
+  static constexpr size_t kUniqueBytesLength = 8;
 
  public:
   static constexpr size_t kLength = kUniqueBytesLength + ActorID::kLength;
diff --git a/src/ray/design_docs/id_specification.md b/src/ray/design_docs/id_specification.md
index 3ae9d5bb3..baf1aad61 100644
--- a/src/ray/design_docs/id_specification.md
+++ b/src/ray/design_docs/id_specification.md
@@ -5,17 +5,17 @@ Ray ID Specification
  high bits                                                                           low bits
 <--------------------------------------------------------------------------------------------
 
-                                                                                   4B
+                                                                                   2B
                                                                           +-----------------+
-                                                                          |   unique bytes  |  JobID     4B
+                                                                          |   unique bytes  |  JobID     2B
                                                                           +-----------------+
 
-                                                                 4B                4B
+                                                                 4B                2B
                                                         +-----------------+-----------------+
-                                                        |   unique bytes  |       JobID     |  ActorID   8B
+                                                        |   unique bytes  |       JobID     |  ActorID   6B
                                                         +-----------------+-----------------+
 
-                                        6B                               8B
+                                        8B                               6B
                             +---------------------------+-----------------------------------+
                             |       unique bytes        |               ActorID             |  TaskID   14B
                             +---------------------------+-----------------------------------+
@@ -26,14 +26,14 @@ Ray ID Specification
 +---------------------------+---------------------------------------------------------------+
 
 ```
-#### JobID (4 bytes)
-`JobID` is generated by `GCS` to ensure uniqueness. Its length is 4 bytes.
+#### JobID (2 bytes)
+`JobID` is generated by `GCS` to ensure uniqueness. Its length is 2 bytes.
 
 #### ActorID (8 bytes)
 An `ActorID` contains two parts: 1) 4 unique bytes, and 2) its `JobID`.
 
 #### TaskID (14 bytes)
-A `TaskID` contains two parts: 1) 6 unique bytes, and 2) its `ActorID`.  
+A `TaskID` contains two parts: 1) 8 unique bytes, and 2) its `ActorID`.  
 If the task is a normal task or a driver task, the part 2 is its dummy actor id.
 
 The following table shows the layouts of all kinds of task id.