diff --git a/CHANGELOG.md b/CHANGELOG.md
index 26f4e9b6..694ed0fc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,7 +8,8 @@
   - Added function `vmaGetMemoryWin32Handle2` offering extra parameter `VkExternalMemoryHandleTypeFlagBits handleType`.
 - Added `VMA_VERSION` macro with library version number (#507).
 - Improvements in the algorithm choosing memory type when `VMA_MEMORY_USAGE_AUTO*` is used (#520).
-- Fixes for compatibility with C++20 modules on Clang 21 and GCC15 (#513, #514).
+- Fixed compatibility with C++20 modules on Clang 21 and GCC15 (#513, #514).
+- Fixed race condition in defragmentation (#529, #313).
 - Other fixes and improvements, including compatibility with various platforms and compilers, improvements in documentation, sample application, and tests.
 
 # 3.3.0 (2025-05-12)
diff --git a/include/vk_mem_alloc.h b/include/vk_mem_alloc.h
index 24792855..3934de34 100644
--- a/include/vk_mem_alloc.h
+++ b/include/vk_mem_alloc.h
@@ -12221,6 +12221,8 @@ VmaDefragmentationContext_T::VmaDefragmentationContext_T(
         m_BlockVectorCount = 1;
         m_PoolBlockVector = &info.pool->m_BlockVector;
         m_pBlockVectors = &m_PoolBlockVector;
+
+        VmaMutexLockWrite lock(m_PoolBlockVector->m_Mutex, hAllocator->m_UseMutex);
         m_PoolBlockVector->SetIncrementalSort(false);
         m_PoolBlockVector->SortByFreeSize();
     }
@@ -12234,6 +12236,7 @@ VmaDefragmentationContext_T::VmaDefragmentationContext_T(
             VmaBlockVector* vector = m_pBlockVectors[i];
             if (vector != VMA_NULL)
             {
+                VmaMutexLockWrite lock(vector->m_Mutex, hAllocator->m_UseMutex);
                 vector->SetIncrementalSort(false);
                 vector->SortByFreeSize();
             }
@@ -12264,6 +12267,7 @@ VmaDefragmentationContext_T::~VmaDefragmentationContext_T()
 {
     if (m_PoolBlockVector != VMA_NULL)
     {
+        VmaMutexLockWrite lock(m_PoolBlockVector->m_Mutex, m_PoolBlockVector->m_hAllocator->m_UseMutex);
         m_PoolBlockVector->SetIncrementalSort(true);
     }
     else
@@ -12272,7 +12276,10 @@ VmaDefragmentationContext_T::~VmaDefragmentationContext_T()
         {
             VmaBlockVector* vector = m_pBlockVectors[i];
             if (vector != VMA_NULL)
+            {
+                VmaMutexLockWrite lock(vector->m_Mutex, vector->m_hAllocator->m_UseMutex);
                 vector->SetIncrementalSort(true);
+            }
         }
     }
 
@@ -12370,7 +12377,11 @@ VkResult VmaDefragmentationContext_T::DefragmentPassEnd(VmaDefragmentationPassMo
         {
         case VMA_DEFRAGMENTATION_MOVE_OPERATION_COPY:
         {
-            uint8_t mapCount = move.srcAllocation->SwapBlockAllocation(vector->m_hAllocator, move.dstTmpAllocation);
+            uint8_t mapCount = 0;
+            {
+                VmaMutexLockWrite swapLock(vector->GetMutex(), vector->GetAllocator()->m_UseMutex);
+                mapCount = move.srcAllocation->SwapBlockAllocation(vector->m_hAllocator, move.dstTmpAllocation);
+            }
             if (mapCount > 0)
             {
                 allocator = vector->m_hAllocator;