diff --git a/src/Promotion.jl b/src/Promotion.jl
index 3fb5b7dc..3b6af43a 100644
--- a/src/Promotion.jl
+++ b/src/Promotion.jl
@@ -161,7 +161,7 @@ function Base.promote_rule{S1,S2,D,U1,U2}(::Type{Quantity{S1,D,U1}},
 
     p = promote_unit(U1(), U2())
     numtype = promote_type(S1,S2,
-        typeof(convfact(p,U1())), typeof(convfact(p,U2())))
+        promote_type(typeof(convfact(p,U1())), typeof(convfact(p,U2()))))
     if !isunitless(p)
         if U1 <: ContextUnits && U2 <: ContextUnits
             up1 = upreferred(U1())
diff --git a/src/Unitful.jl b/src/Unitful.jl
index f6ff95a1..048ee688 100644
--- a/src/Unitful.jl
+++ b/src/Unitful.jl
@@ -44,7 +44,8 @@ const promotion = Dict{Symbol,Unit}()
 include("User.jl")
 const NoUnits = FreeUnits{(), Dimensions{()}}()
 const NoDims = Dimensions{()}()
-@inline isunitless{N}(::Units{N}) = N == ()
+isunitless(::Units) = false
+isunitless(::Units{()}) = true
 
 (y::FreeUnits)(x::Number) = uconvert(y,x)
 (y::ContextUnits)(x::Number) = uconvert(y,x)