diff --git a/src/GroupRings.jl b/src/GroupRings.jl
index dad9466..029d79a 100644
--- a/src/GroupRings.jl
+++ b/src/GroupRings.jl
@@ -318,12 +318,12 @@ end
 function mul!{T}(result::AbstractVector{T}, X::AbstractVector, Y::AbstractVector, pm::Array{Int,2})
    z = zero(T)
    result .= z
-   for (j,y) in enumerate(Y)
-      if y != z
-         for (i, index) in enumerate(pm[:,j])
+   for j in eachindex(Y)
+      if Y[j] != z
+         for i in 1:size(pm,1)
             if X[i] != z
-               index == 0 && throw(ArgumentError("The product don't seem to be supported on basis!"))
-               result[index] += X[i]*y
+               pm[i,j] == 0 && throw(ArgumentError("The product don't seem to be supported on basis!"))
+               result[pm[i,j]] += X[i]*Y[j]
             end
          end
       end