diff --git a/kong/clustering/services/sync/rpc.lua b/kong/clustering/services/sync/rpc.lua
index 3bcd515520f..771e992d9d1 100644
--- a/kong/clustering/services/sync/rpc.lua
+++ b/kong/clustering/services/sync/rpc.lua
@@ -23,7 +23,6 @@ local MAX_RETRY = 5
 
 local assert = assert
 local ipairs = ipairs
-local sub = string.sub
 local ngx_null = ngx.null
 local ngx_log = ngx.log
 local ngx_ERR = ngx.ERR
@@ -60,17 +59,6 @@ local function get_current_version()
 end
 
 
-local is_valid_version
-do
-  local VER_PREFIX = "v02_"
-
-  -- version string must start with 'v02_'
-  is_valid_version = function(v)
-    return sub(v, 1, 4) == VER_PREFIX
-  end
-end
-
-
 function _M:init_cp(manager)
   local purge_delay = manager.conf.cluster_data_plane_purge_delay
 
@@ -118,7 +106,7 @@ function _M:init_cp(manager)
     end
 
     --  string comparison effectively does the same as number comparison
-    if not is_valid_version(default_namespace_version) or
+    if not self.strategy:is_valid_version(default_namespace_version) or
        default_namespace_version ~= latest_version then
       return full_sync_result()
     end
diff --git a/kong/clustering/services/sync/strategies/postgres.lua b/kong/clustering/services/sync/strategies/postgres.lua
index 20e594d92f3..06da15cabdc 100644
--- a/kong/clustering/services/sync/strategies/postgres.lua
+++ b/kong/clustering/services/sync/strategies/postgres.lua
@@ -2,12 +2,15 @@ local _M = {}
 local _MT = { __index = _M }
 
 
+local sub = string.sub
 local fmt = string.format
 local ngx_null = ngx.null
 
 
 -- version string should look like: "v02_0000"
-local VERSION_FMT = "v02_%028x"
+local VER_PREFIX = "v02_"
+local VER_PREFIX_LEN = #VER_PREFIX
+local VERSION_FMT = VER_PREFIX .. "%028x"
 
 
 function _M.new(db)
@@ -56,6 +59,11 @@ function _M:get_latest_version()
 end
 
 
+function _M:is_valid_version(str)
+  return sub(str, 1, VER_PREFIX_LEN) == VER_PREFIX
+end
+
+
 function _M:begin_txn()
   return self.connector:query("BEGIN;")
 end