diff --git a/awkward-cpp/src/cpu-kernels/awkward_UnionArray_regular_index_getsize.cpp b/awkward-cpp/src/cpu-kernels/awkward_UnionArray_regular_index_getsize.cpp
index 355c88a09b..88d40fa49a 100644
--- a/awkward-cpp/src/cpu-kernels/awkward_UnionArray_regular_index_getsize.cpp
+++ b/awkward-cpp/src/cpu-kernels/awkward_UnionArray_regular_index_getsize.cpp
@@ -19,20 +19,20 @@ ERROR awkward_UnionArray_regular_index_getsize(
   *size = *size + 1;
   return success();
 }
-ERROR awkward_UnionArray8_regular_index_getsize(
+ERROR awkward_UnionArray64_regular_index_getsize(
   int64_t* size,
-  const int8_t* fromtags,
+  const int64_t* fromtags,
   int64_t length) {
-  return awkward_UnionArray_regular_index_getsize<int8_t>(
+  return awkward_UnionArray_regular_index_getsize<int64_t>(
     size,
     fromtags,
     length);
 }
-ERROR awkward_UnionArray64_regular_index_getsize(
+ERROR awkward_UnionArray8_regular_index_getsize(
   int64_t* size,
-  const int64_t* fromtags,
+  const int8_t* fromtags,
   int64_t length) {
-  return awkward_UnionArray_regular_index_getsize<int64_t>(
+  return awkward_UnionArray_regular_index_getsize<int8_t>(
     size,
     fromtags,
     length);
diff --git a/kernel-specification.yml b/kernel-specification.yml
index eafb308c05..d95b40a01d 100644
--- a/kernel-specification.yml
+++ b/kernel-specification.yml
@@ -3514,15 +3514,15 @@ kernels:
 
   - name: awkward_UnionArray_regular_index_getsize
     specializations:
-      - name: awkward_UnionArray8_regular_index_getsize
+      - name: awkward_UnionArray64_regular_index_getsize
         args:
           - {name: size, type: "List[int64_t]", dir: out}
-          - {name: fromtags, type: "Const[List[int8_t]]", dir: in, role: UnionArray-tags}
+          - {name: fromtags, type: "Const[List[int64_t]]", dir: in, role: UnionArray-tags}
           - {name: length, type: "int64_t", dir: in, role: default}
-      - name: awkward_UnionArray64_regular_index_getsize
+      - name: awkward_UnionArray8_regular_index_getsize
         args:
           - {name: size, type: "List[int64_t]", dir: out}
-          - {name: fromtags, type: "Const[List[int64_t]]", dir: in, role: UnionArray-tags}
+          - {name: fromtags, type: "Const[List[int8_t]]", dir: in, role: UnionArray-tags}
           - {name: length, type: "int64_t", dir: in, role: default}
     description: null
     definition: |