diff --git a/NEWS.md b/NEWS.md
index 75460bd6bb..514ea3bf62 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -151,6 +151,8 @@ unit = "s")
 
 8. Change of `c.POSIXct` method planned for R 4.1.0 impacted `foverlaps` function that could raise `'origin' must be supplied` error. Fix for planned change has been provided in [#4428](https://github.com/Rdatatable/data.table/pull/4428).
 
+9. `data.table::update.dev.pkg()` now unloads the `data.table` namespace to alleviate a DLL lock issue on Windows, [#4403](https://github.com/Rdatatable/data.table/issues/4403). Thanks to @drag5 for reporting.
+
 
 # data.table [v1.12.8](https://github.com/Rdatatable/data.table/milestone/15?closed=1)  (09 Dec 2019)
 
diff --git a/R/devel.R b/R/devel.R
index 8db74e47ce..b0dfb71858 100644
--- a/R/devel.R
+++ b/R/devel.R
@@ -7,7 +7,7 @@ dcf.lib = function(pkg, field, lib.loc=NULL){
   if (nzchar(dcf)) read.dcf(dcf, fields=field)[1L] else NA_character_
 }
 
-dcf.repo = function(pkg, repo, field, type){
+dcf.repo = function(pkg, repo, field, type) {
   # get DESCRIPTION metadata field from remote PACKAGES file
   stopifnot(is.character(pkg), is.character(field), length(pkg)==1L, length(field)==1L, is.character(repo), length(repo)==1L, field!="Package")
   idx = file(file.path(contrib.url(repo, type=type),"PACKAGES"))
@@ -17,22 +17,33 @@ dcf.repo = function(pkg, repo, field, type){
   dcf[dcf[,"Package"]==pkg, field][[1L]]
 }
 
-update.dev.pkg = function(object="data.table", repo="https://Rdatatable.gitlab.io/data.table", field="Revision", type=getOption("pkgType"), lib=NULL, ...){
+update.dev.pkg = function(object="data.table", repo="https://Rdatatable.gitlab.io/data.table", field="Revision", type=getOption("pkgType"), lib=NULL, ...) {
+  # this works for any package, not just data.table
   pkg = object
   # perform package upgrade when new Revision present
   stopifnot(is.character(pkg), length(pkg)==1L, !is.na(pkg),
             is.character(repo), length(repo)==1L, !is.na(repo),
             is.character(field), length(field)==1L, !is.na(field),
             is.null(lib) || (is.character(lib) && length(lib)==1L && !is.na(lib)))
+  # get Revision field from remote repository PACKAGES file
   una = is.na(ups<-dcf.repo(pkg, repo, field, type))
-  upg = una | !identical(ups, dcf.lib(pkg, field, lib.loc=lib))
-  if (upg) utils::install.packages(pkg, repos=repo, type=type, lib=lib, ...)
-  if (una) cat(sprintf("No commit information found in DESCRIPTION file for %s package. Unsure '%s' is correct field name in PACKAGES file in your devel repository '%s'.\n", pkg, field, file.path(repo, "src","contrib","PACKAGES")))
-  cat(sprintf("R %s package %s %s (%s)\n",
-              pkg,
-              c("is up-to-date at","has been updated to")[upg+1L],
-              dcf.lib(pkg, field, lib.loc=lib),
-              utils::packageVersion(pkg, lib.loc=lib)))
+  if (una)
+    cat(sprintf("No revision information found in DESCRIPTION file for %s package. Unsure '%s' is correct field in PACKAGES file in your package repository '%s'. Otherwise package will be re-installed every time, proceeding to installation.\n",
+                pkg, field, contrib.url(repo, type=type)))
+  # see if Revision is different then currently installed Revision, note that installed package will have Revision info only when it was installed from remote devel repo
+  upg = una || !identical(ups, dcf.lib(pkg, field, lib.loc=lib))
+  # update.dev.pkg fails on windows R 4.0.0, we have to unload package namespace before installing new version #4403
+  on.exit({
+    if (upg) {
+      unloadNamespace(pkg) ## hopefully will release dll lock on Windows
+      utils::install.packages(pkg, repos=repo, type=type, lib=lib, ...)
+    }
+    cat(sprintf("R %s package %s %s (%s)\n",
+                pkg,
+                c("is up-to-date at","has been updated to")[upg+1L],
+                unname(read.dcf(system.file("DESCRIPTION", package=pkg, lib.loc=lib, mustWork=TRUE), fields=field)[, field]),
+                utils::packageVersion(pkg, lib.loc=lib)))
+  })
 }
 
 # non-exported utility when using devel version #3272: data.table:::.git()
diff --git a/man/update.dev.pkg.Rd b/man/update.dev.pkg.Rd
index f4802641cc..96f87c296d 100644
--- a/man/update.dev.pkg.Rd
+++ b/man/update.dev.pkg.Rd
@@ -3,15 +3,9 @@
 \alias{update.dev.pkg}
 \title{Perform update of development version of a package}
 \description{
-  It will download and install package from devel repository only when new commit is
-  available there, otherwise only PACKAGES file is transferred. Defaults are set to update \code{data.table}, other
-  packages can be used. Their repository has to include git commit
-  information in PACKAGES file.
+  It will download and install package from devel repository only when new commit is available there, otherwise only PACKAGES file is transferred. Defaults are set to update \code{data.table}, other packages can be used as well. Their repository has to include git commit information in PACKAGES file.
 }
-
-\usage{\method{update}{dev.pkg}(object="data.table",
-repo="https://Rdatatable.gitlab.io/data.table", field="Revision",
-type=getOption("pkgType"), lib=NULL, \dots)
+  \usage{\method{update}{dev.pkg}(object="data.table", repo="https://Rdatatable.gitlab.io/data.table", field="Revision", type=getOption("pkgType"), lib=NULL, \dots)
 }
 \arguments{
   \item{object}{ character scalar, package name. }
@@ -25,9 +19,10 @@ type=getOption("pkgType"), lib=NULL, \dots)
   \item{\dots}{ passed to \code{\link[utils]{install.packages}}. }
 }
 \details{
-  In case if devel repository does not provide package binaries user has
-  have development tools installed for package compilation to use
-  this function.
+  In case if a devel repository does not provide binaries user will need development tools installed for package compilation, like \emph{Rtools} on Windows, and eventually set \code{type="source"}.
+}
+\note{
+  Package namespace is unloaded before attempting to install newer version.
 }
 \value{
   NULL.