diff --git a/Data/Numbers/Primes.hs b/Data/Numbers/Primes.hs
--- a/Data/Numbers/Primes.hs
+++ b/Data/Numbers/Primes.hs
@@ -52,14 +52,15 @@
 {-# SPECIALISE wheelSieve :: Int -> [Integer] #-}
 
 -- |
--- Checks whether a given positive number is prime.
+-- Checks whether a given number is prime.
 -- 
 -- This function uses trial division to check for divisibility with
 -- all primes below the square root of the given number. It is
 -- impractical for numbers with a very large smallest prime factor.
 -- 
 isPrime :: Integral int => int -> Bool
-isPrime n = primeFactors n == [n]
+isPrime n | n > 1     = primeFactors n == [n]
+          | otherwise = False
 
 {-# SPECIALISE isPrime :: Int     -> Bool #-}
 {-# SPECIALISE isPrime :: Integer -> Bool #-}
diff --git a/primes.cabal b/primes.cabal
--- a/primes.cabal
+++ b/primes.cabal
@@ -1,5 +1,5 @@
 Name:          primes
-Version:       0.2.0.0
+Version:       0.2.1.0
 Cabal-Version: >= 1.6
 Synopsis:      Efficient, purely functional generation of prime numbers
 Description: