diff --git a/Makefile-rpm-ostree.am b/Makefile-rpm-ostree.am
index e1adc585..ddc04b0c 100644
--- a/Makefile-rpm-ostree.am
+++ b/Makefile-rpm-ostree.am
@@ -55,7 +55,7 @@ rpm_ostree_SOURCES = src/app/main.cxx \
 	src/app/rpmostree-libbuiltin.h \
 	src/app/rpmostree-polkit-agent.cxx \
 	src/app/rpmostree-polkit-agent.h \
-	src/app/rpmostree-builtin-kargs.c \
+	src/app/rpmostree-builtin-kargs.cxx \
 	src/app/rpmostree-compose-builtin-tree.cxx \
 	src/app/rpmostree-composeutil.cxx \
 	src/app/rpmostree-composeutil.h \
diff --git a/src/app/rpmostree-builtin-kargs.c b/src/app/rpmostree-builtin-kargs.cxx
similarity index 98%
rename from src/app/rpmostree-builtin-kargs.c
rename to src/app/rpmostree-builtin-kargs.cxx
index ce84c78c..3b9a6771 100644
--- a/src/app/rpmostree-builtin-kargs.c
+++ b/src/app/rpmostree-builtin-kargs.cxx
@@ -123,7 +123,7 @@ kernel_arg_handle_editor (const char     *input_kernel_arg,
     }
 
   /* Transfer the ownership to a new string, so we can remove the trailing spaces */
-  g_autofree char *kernel_args_str = g_string_free (g_steal_pointer (&kernel_arg_buf), FALSE);
+  g_autofree char *kernel_args_str = g_string_free (util::move_nullify (kernel_arg_buf), FALSE);
   g_strchomp (kernel_args_str);
 
   g_autoptr(OstreeKernelArgs) input_kargs = ostree_kernel_args_from_string (kernel_args_str);
@@ -152,7 +152,7 @@ kernel_arg_handle_editor (const char     *input_kernel_arg,
       return FALSE;
     }
 
-  *out_kernel_arg = g_steal_pointer (&kernel_args_str);
+  *out_kernel_arg = util::move_nullify (kernel_args_str);
 
   return TRUE;
 }