diff --git a/vulkan/vCmdBuffer.pas b/vulkan/vCmdBuffer.pas
index dc71908a..836907c1 100644
--- a/vulkan/vCmdBuffer.pas
+++ b/vulkan/vCmdBuffer.pas
@@ -715,9 +715,19 @@ begin
  srcb:=FetchHostBuffer(Self,src,byteCount,ord(VK_BUFFER_USAGE_TRANSFER_SRC_BIT));
  Assert(srcb<>nil);
 
+ if (srcb.Foffset+byteCount>srcb.FSize) then
+ begin
+  Assert(False,'FetchHostBuffer:Insufficient buffer size!');
+ end;
+
  dstb:=FetchHostBuffer(Self,dst,byteCount,ord(VK_BUFFER_USAGE_TRANSFER_DST_BIT));
  Assert(dstb<>nil);
 
+ if (dstb.Foffset+byteCount>dstb.FSize) then
+ begin
+  Assert(False,'FetchHostBuffer:Insufficient buffer size!');
+ end;
+
  Inc(cmd_count);
 
  vkBufferMemoryBarrier(cmdbuf,
diff --git a/vulkan/vHostBufferManager.pas b/vulkan/vHostBufferManager.pas
index ee93cea8..cb480450 100644
--- a/vulkan/vHostBufferManager.pas
+++ b/vulkan/vHostBufferManager.pas
@@ -102,14 +102,12 @@ end;
 function _fix_buf_size(sparce:Boolean;var Addr:Pointer;var Size:TVkDeviceSize;usage:TVkFlags):TVkDeviceSize;
 var
  mr:TVkMemoryRequirements;
- pAlign:Pointer;
 begin
  mr:=GetRequirements(sparce,Size,usage,@buf_ext);
 
- pAlign:=AlignDw(Addr,mr.alignment);
- Result:=(Addr-pAlign);
+ Result:=(ptruint(Addr) mod mr.alignment);
 
- Addr:=pAlign;
+ Addr:=Pointer(ptruint(Addr)-Result);
  Size:=Size+Result;
 end;
 
@@ -234,11 +232,11 @@ begin
 
  FHostBufferSet.Lock_wr;
 
- t:=_Find(Addr);
+ t:=_Find(Addr); //find by key
 
  if (t<>nil) then
  begin
-  if (t.FSize<Size) or
+  if (t.FSize<(t.Foffset+Size)) or
      ((t.FUsage and usage)<>usage) then
   begin
    usage:=usage or t.FUsage;
@@ -268,7 +266,7 @@ begin
     Assert(false,'_is_sparce');
   end;
 
-  t.FAddr:=addr;
+  t.FAddr:=addr; //save key
 
   FHostBufferSet.Insert(@t.FAddr);
   t.Acquire(nil);