diff --git a/cpp/src/arrow/testing/random.cc b/cpp/src/arrow/testing/random.cc
index 0614b9822e3b0..d540c2b19e65b 100644
--- a/cpp/src/arrow/testing/random.cc
+++ b/cpp/src/arrow/testing/random.cc
@@ -360,7 +360,7 @@ struct SmallDecimalGenerator {
   std::shared_ptr<Array> MakeRandomArray(int64_t size, double null_probability,
                                          int64_t alignment, MemoryPool* memory_pool) {
     static constexpr int32_t kMaxDigitsInInteger =
-        std::is_same_v<DecimalType, Decimal32Type> ? 9 : 18;    
+        std::is_same_v<DecimalType, Decimal32Type> ? 9 : 18;
     static_assert(
         kMaxDigitsInInteger >= DecimalType::kByteWidth,
         "inconsistent decimal metadata: kMaxPrecision doesn't match kByteWidth");