diff --git a/src/chunks.jl b/src/chunks.jl
index 1b57ee6e..e5b28360 100644
--- a/src/chunks.jl
+++ b/src/chunks.jl
@@ -81,7 +81,7 @@ end
 
 function Base.iterate(x::Chunks, i=1)
     i >= length(x.ranges) && return nothing
-    f = File(x.h; startingbyteposition=x.ranges[i], endingbyteposition=(x.ranges[i + 1] - (i != length(x.ranges))), threaded=x.threaded, typemap=x.typemap, tasks=x.tasks, debug=x.debug)
+    f = File(x.h; finalizebuffer=false, startingbyteposition=x.ranges[i], endingbyteposition=(x.ranges[i + 1] - (i != length(x.ranges))), threaded=x.threaded, typemap=x.typemap, tasks=x.tasks, debug=x.debug)
     return f, i + 1
 end
 
diff --git a/src/file.jl b/src/file.jl
index 4b0bf14b..70f5aa5a 100644
--- a/src/file.jl
+++ b/src/file.jl
@@ -220,6 +220,7 @@ function File(source;
 end
 
 function File(h::Header;
+    finalizebuffer=true,
     startingbyteposition=nothing,
     endingbyteposition=nothing,
     limit::Union{Integer, Nothing}=nothing,
@@ -344,7 +345,7 @@ function File(h::Header;
     lookup = Dict(k => v for (k, v) in zip(h.names, columns))
     # for windows, it's particularly finicky about throwing errors when you try to modify an mmapped file
     # so we just want to make sure we finalize the input buffer so users don't run into surprises
-    if Sys.iswindows() && ncols > 0 && !lazystrings(flags[1])
+    if finalizebuffer && Sys.iswindows() && ncols > 0 && !lazystrings(flags[1])
         finalize(buf)
     end
     return File{something(threaded, false)}(h.name, h.names, types, finalrows, ncols, columns, lookup)
diff --git a/src/header.jl b/src/header.jl
index 3b0818f8..9a10ef3a 100644
--- a/src/header.jl
+++ b/src/header.jl
@@ -38,7 +38,7 @@ Checks whether a character or string is valid for use as a delimiter.  If
 Throws an error if `delim` is invalid.
 """
 function checkvaliddelim(delim)
-    delim != nothing && !isvaliddelim(delim) &&
+    delim !== nothing && !isvaliddelim(delim) &&
         throw(ArgumentError("invalid delim argument = '$(escape_string(string(delim)))', "*
                             "the following delimiters are invalid: '\\r', '\\n', '\\0'"))
 end