diff --git a/cpp/src/arrow/ipc/reader.cc b/cpp/src/arrow/ipc/reader.cc
index 5dd01f2015dd7..a60375acb420a 100644
--- a/cpp/src/arrow/ipc/reader.cc
+++ b/cpp/src/arrow/ipc/reader.cc
@@ -254,7 +254,12 @@ class ArrayLoader {
     if (i >= static_cast<int>(variadic_counts->size())) {
       return Status::IOError("variadic_count_index out of range.");
     }
-    return static_cast<size_t>(variadic_counts->Get(i));
+    int64_t count = variadic_counts->Get(i);
+    if (count < 0 || count > std::numeric_limits<int32_t>::max()) {
+      return Status::IOError(
+          "variadic_count must be represenable as a positive int32_t, got ", count, ".");
+    }
+    return static_cast<size_t>(count);
   }
 
   Status GetFieldMetadata(int field_index, ArrayData* out) {
@@ -372,10 +377,10 @@ class ArrayLoader {
     RETURN_NOT_OK(LoadCommon(type.id()));
     RETURN_NOT_OK(GetBuffer(buffer_index_++, &out_->buffers[1]));
 
-    ARROW_ASSIGN_OR_RAISE(auto character_buffer_count,
+    ARROW_ASSIGN_OR_RAISE(auto data_buffer_count,
                           GetVariadicCount(variadic_count_index_++));
-    out_->buffers.resize(character_buffer_count + 2);
-    for (size_t i = 0; i < character_buffer_count; ++i) {
+    out_->buffers.resize(data_buffer_count + 2);
+    for (size_t i = 0; i < data_buffer_count; ++i) {
       RETURN_NOT_OK(GetBuffer(buffer_index_++, &out_->buffers[i + 2]));
     }
     return Status::OK();