diff --git a/src/tensor_operations/tensor_algebra.jl b/src/tensor_operations/tensor_algebra.jl
index 36381d6caf..c5c0b9d70b 100644
--- a/src/tensor_operations/tensor_algebra.jl
+++ b/src/tensor_operations/tensor_algebra.jl
@@ -261,6 +261,12 @@ function directsum_projectors(
   return D1, D2
 end
 
+function directsum_projectors(::Type{<:EmptyNumber}, ::Type{<:EmptyNumber}, ::Index, ::Index, ::Index)
+  error("It is not possible to call directsum on two tensors with element type EmptyNumber.
+  If you are inputting ITensors constructor like ITensor(i, j), try specifying the element type, 
+  e.g. ITensor(Float64, i, j), or filling them with zero value, e.g. ITensor(0.0, i, j).")
+end
+
 function check_directsum_inds(A::ITensor, I, B::ITensor, J)
   a = uniqueinds(A, I)
   b = uniqueinds(B, J)