diff --git a/src/Runic.jl b/src/Runic.jl
index 2031191..f73c52b 100644
--- a/src/Runic.jl
+++ b/src/Runic.jl
@@ -146,6 +146,7 @@ mutable struct Context
     next_sibling::Union{Node, Nothing}
     # parent::Union{Node, Nothing}
     lineage_kinds::Vector{JuliaSyntax.Kind}
+    tmp_buf::IOBuffer
 end
 
 function Context(
@@ -178,6 +179,7 @@ function Context(
     return Context(
         src_str, src_tree, src_io, fmt_io, fmt_tree, quiet, verbose, assert, debug, check,
         diff, filemode, call_depth, indent_level, prev_sibling, next_sibling, lineage_kinds,
+        IOBuffer(),
     )
 end
 
diff --git a/src/chisels.jl b/src/chisels.jl
index 9337ccb..febb243 100644
--- a/src/chisels.jl
+++ b/src/chisels.jl
@@ -557,6 +557,8 @@ end
 # Utilities for IOBuffer #
 ##########################
 
+const backup_buffer = IOBuffer()
+
 # Replace bytes for a node at the current position in the IOBuffer. `size` is the current
 # window for the node, i.e. the number of bytes until the next node starts. If `size` is
 # smaller or larger than the length of `bytes` this method will shift the bytes for
@@ -568,7 +570,8 @@ function replace_bytes!(io::IOBuffer, bytes::Union{String, AbstractVector{UInt8}
         nw = write(io, bytes)
         @assert nb == nw
     else
-        backup = IOBuffer() # TODO: global const (with lock)?
+        # backup = IOBuffer() # TODO: global const (with lock)?
+        backup = truncate(backup_buffer, 0)
         seek(io, pos + size)
         @assert position(io) == pos + size
         nb_written_to_backup = write(backup, io)