diff --git a/bin/prime.py b/bin/prime.py
index 30436d8fd..16f260121 100755
--- a/bin/prime.py
+++ b/bin/prime.py
@@ -18,7 +18,7 @@ def print_sieve(sieve):
     primes = []
     for n, prime in enumerate(sieve):
         if n >= 2 and prime:
-            primes.append(n)
+            primes.append(str(n))
     return ", ".join(primes)
 
 def is_prime(n):