diff --git a/renderdoc/driver/vulkan/vk_debug.cpp b/renderdoc/driver/vulkan/vk_debug.cpp
index 8920dcd80..4ba199737 100644
--- a/renderdoc/driver/vulkan/vk_debug.cpp
+++ b/renderdoc/driver/vulkan/vk_debug.cpp
@@ -754,14 +754,6 @@ VulkanDebugManager::VulkanDebugManager(WrappedVulkan *driver)
   {
     m_ReadbackWindow.Create(driver, dev, STAGE_BUFFER_BYTE_SIZE, 1, GPUBuffer::eGPUBufferReadback);
   }
-  else
-  {
-    m_ReadbackWindow.Create(driver, dev, 256 * 1024 * 1024ULL, 1, GPUBuffer::eGPUBufferReadback);
-
-    vkr = ObjDisp(dev)->MapMemory(Unwrap(dev), Unwrap(m_ReadbackWindow.mem), 0, VK_WHOLE_SIZE, 0,
-                                  (void **)&m_ReadbackPtr);
-    RDCASSERTEQUAL(vkr, VK_SUCCESS);
-  }
 }
 
 VulkanDebugManager::~VulkanDebugManager()
@@ -2167,12 +2159,20 @@ void VulkanDebugManager::FillWithDiscardPattern(VkCommandBuffer cmd, DiscardType
   DoPipelineBarrier(cmd, 1, &dstimBarrier);
 }
 
-void VulkanDebugManager::InitReadbackBuffer()
+void VulkanDebugManager::InitReadbackBuffer(VkDeviceSize sz)
 {
-  if(m_ReadbackWindow.buf == VK_NULL_HANDLE)
+  if(m_ReadbackWindow.buf == VK_NULL_HANDLE || m_ReadbackWindow.sz < sz)
   {
+    if(m_ReadbackWindow.buf != VK_NULL_HANDLE)
+    {
+      m_ReadbackWindow.Destroy();
+    }
+
     VkDevice dev = m_pDriver->GetDev();
-    m_ReadbackWindow.Create(m_pDriver, dev, 256 * 1024 * 1024ULL, 1, GPUBuffer::eGPUBufferReadback);
+    m_ReadbackWindow.Create(m_pDriver, dev, AlignUp(sz, (VkDeviceSize)4096), 1,
+                            GPUBuffer::eGPUBufferReadback);
+
+    RDCLOG("Allocating readback window of %llu bytes", m_ReadbackWindow.sz);
 
     VkResult vkr = ObjDisp(dev)->MapMemory(Unwrap(dev), Unwrap(m_ReadbackWindow.mem), 0,
                                            VK_WHOLE_SIZE, 0, (void **)&m_ReadbackPtr);
diff --git a/renderdoc/driver/vulkan/vk_debug.h b/renderdoc/driver/vulkan/vk_debug.h
index 339512525..fcf0d8230 100644
--- a/renderdoc/driver/vulkan/vk_debug.h
+++ b/renderdoc/driver/vulkan/vk_debug.h
@@ -72,7 +72,7 @@ public:
                               VkImageLayout curLayout, VkImageSubresourceRange discardRange,
                               VkRect2D discardRect);
 
-  void InitReadbackBuffer();
+  void InitReadbackBuffer(VkDeviceSize sz);
   byte *GetReadbackPtr() { return m_ReadbackPtr; }
   VkBuffer GetReadbackBuffer() { return m_ReadbackWindow.buf; }
   VkDeviceMemory GetReadbackMemory() { return m_ReadbackWindow.mem; }
diff --git a/renderdoc/driver/vulkan/wrappers/vk_queue_funcs.cpp b/renderdoc/driver/vulkan/wrappers/vk_queue_funcs.cpp
index 8f0b9d51d..a2c22cfe6 100644
--- a/renderdoc/driver/vulkan/wrappers/vk_queue_funcs.cpp
+++ b/renderdoc/driver/vulkan/wrappers/vk_queue_funcs.cpp
@@ -1055,7 +1055,7 @@ VkResult WrappedVulkan::vkQueueSubmit(VkQueue queue, uint32_t submitCount,
             RDCDEBUG("Reading back %s with GPU for comparison",
                      ToStr(record->GetResourceID()).c_str());
 
-            GetDebugManager()->InitReadbackBuffer();
+            GetDebugManager()->InitReadbackBuffer(state.mapOffset + state.mapSize);
 
             // immediately issue a command buffer to copy back the data. We do that on this queue to
             // avoid complexity with synchronising with another queue, but the transfer queue if