diff --git a/src/evalvars.c b/src/evalvars.c
index 6facbeb..f18b516 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -4100,7 +4100,7 @@
 
 	    // Modifying a final variable with a List value using the "+="
 	    // operator is allowed.  For other types, it is not allowed.
-	    if (((flags & ASSIGN_FOR_LOOP) == 0
+	    if ((((flags & ASSIGN_FOR_LOOP) == 0 || (flags & ASSIGN_DECL) == 0)
 			&& ((flags & ASSIGN_COMPOUND_OP) == 0
 			    || !type_inplace_modifiable))
 				 ? var_check_permission(di, name) == FAIL
diff --git a/src/testdir/test_eval_stuff.vim b/src/testdir/test_eval_stuff.vim
index a346399..1b17108 100644
--- a/src/testdir/test_eval_stuff.vim
+++ b/src/testdir/test_eval_stuff.vim
Binary files differ
diff --git a/src/version.c b/src/version.c
index ce5894f..1b7e423 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    665,
+/**/
     664,
 /**/
     663,