diff --git a/DESCRIPTION b/DESCRIPTION
index 3b59d1a..cc061d9 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: mlr3db
 Title: Data Base Backend for 'mlr3'
-Version: 0.5.1-9000
+Version: 0.5.2
 Authors@R:
     person(given = "Michel",
            family = "Lang",
@@ -21,7 +21,7 @@ Depends:
     mlr3 (>= 0.13.0),
     R (>= 3.1.0)
 Imports:
-    R6,
+    R6 (>= 2.4.0),
     backports,
     checkmate,
     data.table,
diff --git a/NEWS.md b/NEWS.md
index 85fb616..0830522 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -2,6 +2,7 @@
 
 - Bugfix: `DataBackendDuckDB` calculated missing values incorrectly.
 - Compatibility with future versions of `dbplyr` (#35).
+- Finalizers are now private
 
 # mlr3db 0.5.1
 
diff --git a/R/DataBackendDplyr.R b/R/DataBackendDplyr.R
index 03a21ce..d7bc52d 100644
--- a/R/DataBackendDplyr.R
+++ b/R/DataBackendDplyr.R
@@ -120,16 +120,6 @@ DataBackendDplyr = R6Class("DataBackendDplyr", inherit = DataBackend, cloneable
       self$connector = assert_function(connector, args = character(), null.ok = TRUE)
     },
 
-    #' @description
-    #' Finalizer which disconnects from the database.
-    #' This is called during garbage collection of the instance.
-    #' @return `logical(1)`, the return value of [DBI::dbDisconnect()].
-    finalize = function() {
-      if (isTRUE(self$valid)) {
-        DBI::dbDisconnect(private$.data$src$con)
-      }
-    },
-
     #' @description
     #' Returns a slice of the data.
     #' Calls [dplyr::filter()] and [dplyr::select()] on the table and converts it to a [data.table::data.table()].
@@ -271,6 +261,16 @@ DataBackendDplyr = R6Class("DataBackendDplyr", inherit = DataBackend, cloneable
   ),
 
   private = list(
+    # @description
+    # Finalizer which disconnects from the database.
+    # This is called during garbage collection of the instance.
+    # @return `logical(1)`, the return value of [DBI::dbDisconnect()].
+    finalize = function() {
+      if (isTRUE(self$valid)) {
+        DBI::dbDisconnect(private$.data$src$con)
+      }
+    },
+
     .calculate_hash = function() {
       private$.reconnect()
       calculate_hash(private$.data)
diff --git a/R/DataBackendDuckDB.R b/R/DataBackendDuckDB.R
index 03d0dd3..a043a6f 100644
--- a/R/DataBackendDuckDB.R
+++ b/R/DataBackendDuckDB.R
@@ -73,16 +73,6 @@ DataBackendDuckDB = R6Class("DataBackendDuckDB", inherit = DataBackend, cloneabl
 
     },
 
-    #' @description
-    #' Finalizer which disconnects from the database.
-    #' This is called during garbage collection of the instance.
-    #' @return `logical(1)`, the return value of [DBI::dbDisconnect()].
-    finalize = function() {
-      if (isTRUE(self$valid)) {
-        DBI::dbDisconnect(private$.data, shutdown = TRUE)
-      }
-    },
-
     #' @description
     #' Returns a slice of the data.
     #'
@@ -243,6 +233,16 @@ DataBackendDuckDB = R6Class("DataBackendDuckDB", inherit = DataBackend, cloneabl
   ),
 
   private = list(
+    # @description
+    # Finalizer which disconnects from the database.
+    # This is called during garbage collection of the instance.
+    # @return `logical(1)`, the return value of [DBI::dbDisconnect()].
+    finalize = function() {
+      if (isTRUE(self$valid)) {
+        DBI::dbDisconnect(private$.data, shutdown = TRUE)
+      }
+    },
+
     .calculate_hash = function() {
       private$.reconnect()
       calculate_hash(private$.data@driver@dbdir)
diff --git a/man/DataBackendDplyr.Rd b/man/DataBackendDplyr.Rd
index f972d15..5db4c26 100644
--- a/man/DataBackendDplyr.Rd
+++ b/man/DataBackendDplyr.Rd
@@ -94,7 +94,6 @@ Returns the result of \code{\link[DBI:dbIsValid]{DBI::dbIsValid()}} otherwise.}
 \subsection{Public methods}{
 \itemize{
 \item \href{#method-DataBackendDplyr-new}{\code{DataBackendDplyr$new()}}
-\item \href{#method-DataBackendDplyr-finalize}{\code{DataBackendDplyr$finalize()}}
 \item \href{#method-DataBackendDplyr-data}{\code{DataBackendDplyr$data()}}
 \item \href{#method-DataBackendDplyr-head}{\code{DataBackendDplyr$head()}}
 \item \href{#method-DataBackendDplyr-distinct}{\code{DataBackendDplyr$distinct()}}
@@ -160,20 +159,6 @@ To protect your credentials, it is recommended to use the \CRANpkg{secret} packa
 }
 }
 \if{html}{\out{<hr>}}
-\if{html}{\out{<a id="method-DataBackendDplyr-finalize"></a>}}
-\if{latex}{\out{\hypertarget{method-DataBackendDplyr-finalize}{}}}
-\subsection{Method \code{finalize()}}{
-Finalizer which disconnects from the database.
-This is called during garbage collection of the instance.
-\subsection{Usage}{
-\if{html}{\out{<div class="r">}}\preformatted{DataBackendDplyr$finalize()}\if{html}{\out{</div>}}
-}
-
-\subsection{Returns}{
-\code{logical(1)}, the return value of \code{\link[DBI:dbDisconnect]{DBI::dbDisconnect()}}.
-}
-}
-\if{html}{\out{<hr>}}
 \if{html}{\out{<a id="method-DataBackendDplyr-data"></a>}}
 \if{latex}{\out{\hypertarget{method-DataBackendDplyr-data}{}}}
 \subsection{Method \code{data()}}{
diff --git a/man/DataBackendDuckDB.Rd b/man/DataBackendDuckDB.Rd
index 98c32de..bee586b 100644
--- a/man/DataBackendDuckDB.Rd
+++ b/man/DataBackendDuckDB.Rd
@@ -56,7 +56,6 @@ Returns the result of \code{\link[DBI:dbIsValid]{DBI::dbIsValid()}} otherwise.}
 \subsection{Public methods}{
 \itemize{
 \item \href{#method-DataBackendDuckDB-new}{\code{DataBackendDuckDB$new()}}
-\item \href{#method-DataBackendDuckDB-finalize}{\code{DataBackendDuckDB$finalize()}}
 \item \href{#method-DataBackendDuckDB-data}{\code{DataBackendDuckDB$data()}}
 \item \href{#method-DataBackendDuckDB-head}{\code{DataBackendDuckDB$head()}}
 \item \href{#method-DataBackendDuckDB-distinct}{\code{DataBackendDuckDB$distinct()}}
@@ -121,20 +120,6 @@ To protect your credentials, it is recommended to use the \CRANpkg{secret} packa
 }
 }
 \if{html}{\out{<hr>}}
-\if{html}{\out{<a id="method-DataBackendDuckDB-finalize"></a>}}
-\if{latex}{\out{\hypertarget{method-DataBackendDuckDB-finalize}{}}}
-\subsection{Method \code{finalize()}}{
-Finalizer which disconnects from the database.
-This is called during garbage collection of the instance.
-\subsection{Usage}{
-\if{html}{\out{<div class="r">}}\preformatted{DataBackendDuckDB$finalize()}\if{html}{\out{</div>}}
-}
-
-\subsection{Returns}{
-\code{logical(1)}, the return value of \code{\link[DBI:dbDisconnect]{DBI::dbDisconnect()}}.
-}
-}
-\if{html}{\out{<hr>}}
 \if{html}{\out{<a id="method-DataBackendDuckDB-data"></a>}}
 \if{latex}{\out{\hypertarget{method-DataBackendDuckDB-data}{}}}
 \subsection{Method \code{data()}}{
diff --git a/tests/testthat/helper.R b/tests/testthat/helper.R
index 726f67e..bf387cd 100644
--- a/tests/testthat/helper.R
+++ b/tests/testthat/helper.R
@@ -29,7 +29,7 @@ disconnect.SQLiteConnection = function(x) {
 registerS3method("disconnect", "SQLiteConnection", disconnect.SQLiteConnection)
 
 disconnect.DataBackend = function(x) {
-  x$finalize()
+  mlr3misc::get_private(x)$finalize()
 }
 registerS3method("disconnect", "DataBackend", disconnect.DataBackend)