diff --git a/kitty/dnd.c b/kitty/dnd.c
index df56aad42..c1bf7d7f6 100644
--- a/kitty/dnd.c
+++ b/kitty/dnd.c
@@ -18,13 +18,17 @@
 #include <unistd.h>
 #include <errno.h>
 
-static const size_t MIME_LIST_SIZE_CAP = 1024 * 1024;
-static const size_t PRESENT_DATA_CAP = 64 * 1024 * 1024;
+#define DEFAULT_MIME_LIST_SIZE_CAP 1024u * 1024u
+static size_t MIME_LIST_SIZE_CAP = DEFAULT_MIME_LIST_SIZE_CAP;
+#define DEFAULT_PRESENT_DATA_CAP 64 * 1024 * 1024
+static size_t PRESENT_DATA_CAP = DEFAULT_PRESENT_DATA_CAP;
+#define DEFAULT_REMOTE_DRAG_LIMIT 1024 * 1024 * 1024
+static size_t REMOTE_DRAG_LIMIT = DEFAULT_REMOTE_DRAG_LIMIT;
+static PyObject *g_dnd_test_write_func = NULL;
 
 // Utils {{{
 // In test mode, this callable is invoked instead of schedule_write_to_child_if_possible.
 // It receives (window_id: int, data: bytes) and its return value is ignored.
-static PyObject *g_dnd_test_write_func = NULL;
 static void drop_process_queue(Window *w);
 static void drop_pop_request(Window *w);
 
@@ -157,10 +161,13 @@ sanitized_filename_from_url(const char *url) {
 
 
 void
-dnd_set_test_write_func(PyObject *func) {
+dnd_set_test_write_func(PyObject *func, size_t mime_list_size_cap, size_t present_data_cap, size_t remote_drag_limit) {
     (void)machine_id;
-    Py_XDECREF(g_dnd_test_write_func);
+    Py_CLEAR(g_dnd_test_write_func);
     g_dnd_test_write_func = Py_XNewRef(func);
+    MIME_LIST_SIZE_CAP = mime_list_size_cap ? mime_list_size_cap : DEFAULT_MIME_LIST_SIZE_CAP;
+    PRESENT_DATA_CAP = present_data_cap ? present_data_cap : DEFAULT_PRESENT_DATA_CAP;
+    REMOTE_DRAG_LIMIT = remote_drag_limit ? remote_drag_limit : DEFAULT_REMOTE_DRAG_LIMIT;
 }
 
 static int
@@ -1698,7 +1705,6 @@ finish_remote_data(Window *w, size_t item_idx) {
 }
 
 #define mi ds.items[mime_item_idx]
-static size_t REMOTE_DRAG_LIMIT = 1024 * 1024 * 1024;
 
 static void
 populate_dir_entries(Window *w, DragRemoteItem *ri) {
@@ -1736,7 +1742,7 @@ add_payload(Window *w, DragRemoteItem *ri, bool has_more, const uint8_t *payload
             default: {
                 if (ri->data_sz + payload_sz > ri->data_capacity) {
                     size_t cap = MAX(ri->data_capacity * 2, ri->data_sz + payload_sz + 4096);
-                    if (cap > 10 * 1024) abrt(EMFILE);
+                    if (cap > PRESENT_DATA_CAP) abrt(EMFILE);
                     ri->data = realloc(ri->data, cap);
                     if (!ri->data) abrt(ENOMEM);
                     ri->data_capacity = cap;
diff --git a/kitty/dnd.h b/kitty/dnd.h
index 0c355320e..bcf1a0210 100644
--- a/kitty/dnd.h
+++ b/kitty/dnd.h
@@ -21,7 +21,7 @@ void drop_set_status(Window *w, int operation, const char *payload, size_t paylo
 size_t drop_update_mimes(Window *w, const char **allowed_mimes, size_t allowed_mimes_count);
 void drop_dispatch_data(Window *w, const char *mime_type, const char *data, ssize_t sz);
 void drop_finish(Window *w);
-void dnd_set_test_write_func(PyObject *func);
+void dnd_set_test_write_func(PyObject*, size_t, size_t, size_t);
 
 
 typedef enum { DRAG_NOTIFY_ACCEPTED, DRAG_NOTIFY_ACTION_CHANGED, DRAG_NOTIFY_DROPPED, DRAG_NOTIFY_FINISHED } DragNotifyType;
diff --git a/kitty/glfw.c b/kitty/glfw.c
index 8cc092c05..3ba1add98 100644
--- a/kitty/glfw.c
+++ b/kitty/glfw.c
@@ -898,9 +898,11 @@ request_drop_status_update(OSWindow *osw) {
 // DnD testing infrastructure {{{
 
 static PyObject *
-py_dnd_set_test_write_func(PyObject *self UNUSED, PyObject *func) {
+py_dnd_set_test_write_func(PyObject *self UNUSED, PyObject *args) {
+    PyObject *func = Py_None; unsigned mime_list_size_cap = 0, present_data_cap = 0, remote_drag_limit = 0;
+    if (!PyArg_ParseTuple(args, "|OIII", &func, &mime_list_size_cap, &present_data_cap, &remote_drag_limit)) return NULL;
     // Pass None to clear the interceptor and restore normal operation.
-    dnd_set_test_write_func(func == Py_None ? NULL : func);
+    dnd_set_test_write_func(func == Py_None ? NULL : func, mime_list_size_cap, present_data_cap, remote_drag_limit);
     Py_RETURN_NONE;
 }
 
@@ -3355,7 +3357,7 @@ static PyMethodDef module_methods[] = {
     {"glfw_get_monitor_workarea", (PyCFunction)get_monitor_workarea, METH_NOARGS, ""},
     {"glfw_get_monitor_names", (PyCFunction)get_monitor_names, METH_NOARGS, ""},
     {"glfw_primary_monitor_content_scale", (PyCFunction)primary_monitor_content_scale, METH_NOARGS, ""},
-    {"dnd_set_test_write_func", (PyCFunction)py_dnd_set_test_write_func, METH_O, ""},
+    {"dnd_set_test_write_func", (PyCFunction)py_dnd_set_test_write_func, METH_VARARGS, ""},
     METHODB(dnd_test_create_fake_window, METH_NOARGS),
     METHODB(dnd_test_cleanup_fake_window, METH_VARARGS),
     METHODB(dnd_test_set_mouse_pos, METH_VARARGS),