diff --git a/src/multifusion.jl b/src/multifusion.jl
index 1672b37a..3988a0a8 100644
--- a/src/multifusion.jl
+++ b/src/multifusion.jl
@@ -37,7 +37,13 @@ Base.length(::SectorValues{IsingBimodule}) = length(all_isingbimod_objects)
 const IsingBimoduleProdIterator = SectorProductIterator{IsingBimodule}
 ⊗(a::IsingBimodule, b::IsingBimodule) = SectorProductIterator(a, b)
 
-Base.IteratorSize(::Type{IsingBimoduleProdIterator}) = Base.SizeUnknown()
+Base.IteratorSize(::Type{IsingBimoduleProdIterator}) = Base.HasLength()
+function Base.length(x::IsingBimoduleProdIterator)
+    a, b = x.a, x.b
+    a.col == b.row || return 0
+    a.row == b.col && a.row != a.col && return 2
+    return 1
+end
 
 function Base.iterate(iter::IsingBimoduleProdIterator, state = 0)
     a, b = iter.a, iter.b
diff --git a/test/sectors.jl b/test/sectors.jl
index 2e850b14..383e2e5e 100644
--- a/test/sectors.jl
+++ b/test/sectors.jl
@@ -71,6 +71,10 @@ end
 
 @testsuite "Fusion and dimensions" I -> begin
     for a in smallset(I), b in smallset(I)
+        cs = a ⊗ b
+        if Base.IteratorSize(typeof(cs)) !== Base.SizeUnknown()
+            @test length(cs) == length(collect(cs))
+        end
         can_fuse(a, b) || continue
         da = dim(a)
         db = dim(b)