diff --git a/port_prediction.nim b/port_prediction.nim
index 5fca2bd..e6fac14 100644
--- a/port_prediction.nim
+++ b/port_prediction.nim
@@ -84,16 +84,13 @@ proc predictPortRange*(localPort: Port, probedPorts: seq[Port]): seq[Port] =
         return
   # assume symmetric NAT with random port mapping
   randomize()
-  let first = if minPort >= 1024 + 10000:
-    minPort - 10000
+  let first = if maxPort <= uint16.high - RandomPortCount - 1000'u16:
+    maxPort + 1000'u16
   else:
-    1024
-  let last = if maxPort <= uint16.high - 10000:
-    maxPort + 10000
-  else:
-    uint16.high
-  for _ in 1 .. RandomPortCount:
-    result.add(Port(rand(first .. last)))
+    uint16.high - RandomPortCount
+  result = newSeq[Port](RandomPortCount)
+  for i in 0'u16 .. RandomPortCount - 1'u16:
+    result[i] = Port(first + i)
 
 suite "port prediction tests":
   test "single port":