diff --git a/src/encoders/missingness_encoding/missingness_encoding.jl b/src/encoders/missingness_encoding/missingness_encoding.jl
index 848916c..4d3bf2e 100644
--- a/src/encoders/missingness_encoding/missingness_encoding.jl
+++ b/src/encoders/missingness_encoding/missingness_encoding.jl
@@ -35,7 +35,8 @@ function missingness_encoder_fit(
         Char => 'm',
     ),
 )
-    supportedtypes = Union{Char, AbstractString, Number}
+    supportedtypes_list = [Char, AbstractString, Number]
+    supportedtypes = Union{supportedtypes_list...}
 
     # 1. Define feature mapper
     function feature_mapper(col, name)
@@ -50,7 +51,7 @@ function missingness_encoder_fit(
 
         # Ensure label_for_missing keys are valid types
         for possible_col_type in keys(label_for_missing)
-            if !(possible_col_type in union_types(supportedtypes))
+            if !(possible_col_type in supportedtypes_list)
                 throw(ArgumentError(VALID_TYPES_NEW_VAL_ME(possible_col_type)))
             end
         end
@@ -66,7 +67,7 @@ function missingness_encoder_fit(
 
         # Get ancestor type of column
         elgrandtype = nothing
-        for allowed_type in union_types(supportedtypes)
+        for allowed_type in supportedtypes_list
             if col_type <: allowed_type
                 elgrandtype = allowed_type
                 break
diff --git a/src/transformers/cardinality_reducer/cardinality_reducer.jl b/src/transformers/cardinality_reducer/cardinality_reducer.jl
index 1d8f531..18ca84c 100644
--- a/src/transformers/cardinality_reducer/cardinality_reducer.jl
+++ b/src/transformers/cardinality_reducer/cardinality_reducer.jl
@@ -41,7 +41,8 @@ function cardinality_reducer_fit(
         Char => 'O',
     ),
 )   
-    supportedtypes = Union{Char, AbstractString, Number}
+    supportedtypes_list = [Char, AbstractString, Number]
+    supportedtypes = Union{supportedtypes_list...}
 
     # 1. Define feature mapper
     function feature_mapper(col, name)
@@ -57,7 +58,7 @@ function cardinality_reducer_fit(
 
         # Ensure label_for_infrequent keys are valid types
         for possible_col_type in keys(label_for_infrequent)
-            if !(possible_col_type in union_types(supportedtypes))
+            if !(possible_col_type in supportedtypes_list)
                 throw(ArgumentError(VALID_TYPES_NEW_VAL(possible_col_type)))
             end
         end
@@ -71,7 +72,7 @@ function cardinality_reducer_fit(
 
         # Get ancestor type of column
         elgrandtype = nothing
-        for allowed_type in union_types(supportedtypes)
+        for allowed_type in supportedtypes_list
             if col_type <: allowed_type
                 elgrandtype = allowed_type
                 break
diff --git a/src/utils.jl b/src/utils.jl
index de21a05..8ac976c 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -1,3 +1 @@
-# To go from e.g., Union{Integer, String} to (Integer, String)
-union_types(x::Union) = (x.a, union_types(x.b)...)
-union_types(x::Type) = (x,)
\ No newline at end of file
+# add utility functions here
\ No newline at end of file
diff --git a/test/transformers/cardinality_reducer.jl b/test/transformers/cardinality_reducer.jl
index 6670306..4763683 100644
--- a/test/transformers/cardinality_reducer.jl
+++ b/test/transformers/cardinality_reducer.jl
@@ -1,8 +1,6 @@
-using MLJTransforms: union_types, cardinality_reducer_fit, cardinality_reducer_transform
+using MLJTransforms:  cardinality_reducer_fit, cardinality_reducer_transform
+
 
-@testset "Union_types" begin
-    @test union_types(Union{Integer, String}) == (Integer, String)
-end
 
 @testset "Throws errors when needed" begin
     @test_throws ArgumentError begin