diff --git a/src/errors.h b/src/errors.h
index dd1b9fc..6d3d06d 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -2909,7 +2909,8 @@
 	INIT(= N_("E1140: :for argument must be a sequence of lists"));
 EXTERN char e_indexable_type_required[]
 	INIT(= N_("E1141: Indexable type required"));
-// E1142 unused
+EXTERN char e_calling_test_garbagecollect_now_while_v_testing_is_not_set[]
+	INIT(= N_("E1142: Calling test_garbagecollect_now() while v:testing is not set"));
 EXTERN char e_empty_expression_str[]
 	INIT(= N_("E1143: Empty expression: \"%s\""));
 EXTERN char e_command_str_not_followed_by_white_space_str[]
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 917e89f..ff07916 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -2663,6 +2663,12 @@
   call assert_fails('let x=range(1, 4, [])', 'E745:')
 endfunc
 
+func Test_garbagecollect_now_fails()
+  let v:testing = 0
+  call assert_fails('call test_garbagecollect_now()', 'E1142:')
+  let v:testing = 1
+endfunc
+
 func Test_echoraw()
   CheckScreendump
 
diff --git a/src/testing.c b/src/testing.c
index 675eaa2..4e688a7 100644
--- a/src/testing.c
+++ b/src/testing.c
@@ -1153,7 +1153,10 @@
 {
     // This is dangerous, any Lists and Dicts used internally may be freed
     // while still in use.
-    garbage_collect(TRUE);
+    if (!get_vim_var_nr(VV_TESTING))
+	emsg(_(e_calling_test_garbagecollect_now_while_v_testing_is_not_set));
+    else
+	garbage_collect(TRUE);
 }
 
 /*
diff --git a/src/version.c b/src/version.c
index bc956ce..7247ca7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4234,
+/**/
     4233,
 /**/
     4232,