diff --git a/cpp/src/arrow/memory_pool.cc b/cpp/src/arrow/memory_pool.cc
index cf8bf64..2dcfb01 100644
--- a/cpp/src/arrow/memory_pool.cc
+++ b/cpp/src/arrow/memory_pool.cc
@@ -563,7 +563,7 @@ MemoryPool* default_memory_pool() {

 Status jemalloc_set_decay_ms(int ms) {
 #ifdef ARROW_JEMALLOC
-  ssize_t decay_time_ms = static_cast<ssize_t>(ms);
+  size_t decay_time_ms = static_cast<size_t>(ms);

   int err = mallctl("arenas.dirty_decay_ms", nullptr, nullptr, &decay_time_ms,
                     sizeof(decay_time_ms));