diff --git a/src/Primes.jl b/src/Primes.jl
index 8676625..47e6451 100644
--- a/src/Primes.jl
+++ b/src/Primes.jl
@@ -362,7 +362,7 @@ julia> prodfactors(factor(100))
 """
 function prodfactors end
 
-prodfactors(factors::Associative) = prod(p^i for (p, i) in factors)
+prodfactors{K}(factors::Associative{K}) = isempty(factors) ? one(K) : prod(p^i for (p, i) in factors)
 prodfactors(factors::Union{AbstractArray, Set, IntSet}) = prod(factors)
 
 """
diff --git a/test/runtests.jl b/test/runtests.jl
index e73287c..1c7e4ec 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -341,7 +341,8 @@ end
 end
 
 for T in (Int, UInt, BigInt)
-    for n in rand(T(1):T(100000), 10)
+    for n in [T(1); rand(T(2):T(100000), 10)]
+        # for n=T(1), must not error out (#51)
         for C = (Factorization, Vector, Dict)
             @test prodfactors(factor(C, n)) == n
         end