diff --git a/backends/imgui_impl_vulkan.cpp b/backends/imgui_impl_vulkan.cpp
index d8c00e9b..167687ed 100644
--- a/backends/imgui_impl_vulkan.cpp
+++ b/backends/imgui_impl_vulkan.cpp
@@ -22,6 +22,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2021-03-22: Vulkan: Fix mapped memory validation error when buffer sizes are not multiple of VkPhysicalDeviceLimits::nonCoherentAtomSize.
 //  2021-02-18: Vulkan: Change blending equation to preserve alpha in output buffer.
 //  2021-01-27: Vulkan: Added support for custom function load and IMGUI_IMPL_VULKAN_NO_PROTOTYPES by using ImGui_ImplVulkan_LoadFunctions().
 //  2020-11-11: Vulkan: Added support for specifying which subpass to reference during VkPipeline creation.
@@ -343,7 +344,7 @@ static void CreateOrResizeBuffer(VkBuffer& buffer, VkDeviceMemory& buffer_memory
 
     err = vkBindBufferMemory(v->Device, buffer, buffer_memory, 0);
     check_vk_result(err);
-    p_buffer_size = new_size;
+    p_buffer_size = req.size;
 }
 
 static void ImGui_ImplVulkan_SetupRenderState(ImDrawData* draw_data, VkPipeline pipeline, VkCommandBuffer command_buffer, ImGui_ImplVulkanH_FrameRenderBuffers* rb, int fb_width, int fb_height)
@@ -429,9 +430,9 @@ void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer comm
         // Upload vertex/index data into a single contiguous GPU buffer
         ImDrawVert* vtx_dst = NULL;
         ImDrawIdx* idx_dst = NULL;
-        VkResult err = vkMapMemory(v->Device, rb->VertexBufferMemory, 0, vertex_size, 0, (void**)(&vtx_dst));
+        VkResult err = vkMapMemory(v->Device, rb->VertexBufferMemory, 0, rb->VertexBufferSize, 0, (void**)(&vtx_dst));
         check_vk_result(err);
-        err = vkMapMemory(v->Device, rb->IndexBufferMemory, 0, index_size, 0, (void**)(&idx_dst));
+        err = vkMapMemory(v->Device, rb->IndexBufferMemory, 0, rb->IndexBufferSize, 0, (void**)(&idx_dst));
         check_vk_result(err);
         for (int n = 0; n < draw_data->CmdListsCount; n++)
         {
diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index b7e74a61..b18879e8 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -46,6 +46,8 @@ Other Changes:
 - DragScalar: Add default value for v_speed argument to match higher-level functions. (#3922) [@eliasdaler]
 - Backends: DirectX9: calling IDirect3DStateBlock9::Capture() after CreateStateBlock() which appears to
   workaround/fix state restoring issues. Unknown exactly why so, but bit of a cargo-cult fix. (#3857)
+- Backends: Vulkan: Fix mapped memory Vulkan validation error when buffer sizes are not multiple of
+  VkPhysicalDeviceLimits::nonCoherentAtomSize. (#3957) [@AgentX1994]
 - Examples: Vulkan: Rebuild swapchain on VK_SUBOPTIMAL_KHR. (#3881)
 - Docs: Improvements to minor mistakes in documentation comments (#3923) [@ANF-Studios]