diff --git a/src/virtual_lodf_calculations.jl b/src/virtual_lodf_calculations.jl
index 5ae1ced7..314a24f5 100644
--- a/src/virtual_lodf_calculations.jl
+++ b/src/virtual_lodf_calculations.jl
@@ -242,10 +242,9 @@ function _getindex(
         lodf_row[row] = -1.0
         # add slack bus value (zero) and make copy of temp into the cache
         if get_tol(vlodf) > eps()
-            vlodf.cache[row] = make_entries_zero!(deepcopy(lodf_row), get_tol(vlodf))
-        else
-            vlodf.cache[row] = deepcopy(lodf_row)
+            make_entries_zero!(lodf_row, get_tol(vlodf))
         end
+        vlodf.cache[row] = deepcopy(lodf_row)
         return vlodf.cache[row][column]
     end
 end
diff --git a/test/test_virtual_ptdf.jl b/test/test_virtual_ptdf.jl
index fb2d6c57..6ba5d0e6 100644
--- a/test/test_virtual_ptdf.jl
+++ b/test/test_virtual_ptdf.jl
@@ -71,10 +71,12 @@ end
 @testset "Test virtual PTDF with distributed slack" begin
     # get 5 bus system
     sys = PSB.build_system(PSB.PSITestSystems, "c_sys5")
+    bus_number = length(PNM.get_buses(sys))
+    dist_slack = 1 / bus_number * ones(bus_number)
     # compute full PTDF
-    ptdf = PTDF(sys; dist_slack = slack_array)
+    ptdf = PTDF(sys; dist_slack = dist_slack)
     # compute each row of the virtual PTDF and compare values
-    vptdf = VirtualPTDF(sys; dist_slack = slack_array)
+    vptdf = VirtualPTDF(sys; dist_slack = dist_slack)
     for row in 1:size(ptdf.data, 2)
         # evaluate the column (just needs one element)
         vptdf[row, 1]