diff --git a/include/arena.h b/include/arena.h
index b8252c4..ab3b343 100644
--- a/include/arena.h
+++ b/include/arena.h
@@ -56,6 +56,14 @@ public:
 
   // Reset the arena, potentially also releasing committed pages
   void reset();
+
+  // Get the actual used size.
+  // This may differ from the sum of allocations due to alignment requirements.
+  size_t getUsed() const;
+
+  // Get the actual maximum size.
+  // This may be greater than the maxSize passed into init, due to page size alignment.
+  size_t getMaxSize() const;
 private:
   Region m_region;
   size_t m_minSize;
diff --git a/src/arena.cpp b/src/arena.cpp
index d6daa12..2edfe6d 100644
--- a/src/arena.cpp
+++ b/src/arena.cpp
@@ -60,6 +60,20 @@ bool Arena::init(size_t minSize, size_t maxSize)
   return m_region.init(maxSize);
 }
 
+// Get the actual used size.
+// This may differ from the sum of allocations due to alignment requirements.
+size_t Arena::getUsed() const
+{
+  return m_usedSize;
+}
+
+// Get the actual maximum size.
+// This may be greater than the maxSize passed into init, due to page size alignment.
+size_t Arena::getMaxSize() const
+{
+  return m_region.getSize();
+}
+
 std::byte* Arena::alloc(size_t size)
 {
   size_t neededSize = m_usedSize + size;
@@ -70,7 +84,9 @@ std::byte* Arena::alloc(size_t size)
     if (newSize < m_minSize) {
       newSize = m_minSize;
     }
-    m_region.resize(newSize);
+    if (!m_region.resize(newSize)) {
+      return nullptr;
+    }
   }
 
   std::byte* ret = m_region.getAddress() + m_usedSize;
diff --git a/src/region.cpp b/src/region.cpp
index 5fa2200..8e7f9dc 100644
--- a/src/region.cpp
+++ b/src/region.cpp
@@ -93,6 +93,10 @@ bool Region::resize(size_t size)
     return true;
   }
 
+  if (newSize > m_maxSize) {
+    return false;
+  }
+
   if (newSize > m_committedSize) {
     // ---- Growing ----
 #if defined(_WIN32) || defined(_WIN64)
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 6af3497..68887b9 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -15,7 +15,8 @@ enable_testing()
 add_executable(
   mimir_test
   "region_test.cpp"
-)
+  "arena_test.cpp"
+  "test_util.cpp")
 target_link_libraries(
   mimir_test
   GTest::gtest_main
diff --git a/tests/region_test.cpp b/tests/region_test.cpp
index 3f3841f..f52b40c 100644
--- a/tests/region_test.cpp
+++ b/tests/region_test.cpp
@@ -1,25 +1,10 @@
 #include <gtest/gtest.h>
 #include "mimir.h"
 
+#include "test_util.h"
+
 namespace mimir_tests {
 
-void writeData(std::byte* dest, size_t count, int seed)
-{
-  for (int i = 0; i < count; i++) {
-    dest[i] = std::byte((seed * 3162 + i * 63163) % 0xff);
-  }
-}
-
-bool checkData(std::byte* src, size_t count, int seed)
-{
-  for (int i = 0; i < count; i++) {
-    if (src[i] != std::byte((seed * 3162 + i * 63163) % 0xff)) {
-      return false;
-    }
-  }
-  return true;
-}
-
 TEST(Region, InitialState)
 {
   mimir::init();