diff --git a/src/compiler/generic/vm-tran.lisp b/src/compiler/generic/vm-tran.lisp
index a0c1e4f89..983b98ba7 100644
--- a/src/compiler/generic/vm-tran.lisp
+++ b/src/compiler/generic/vm-tran.lisp
@@ -268,7 +268,7 @@
            (let ((data (truly-the (simple-array ,element-type-specifier 1) data)))
              ,(if stringp
                   `(if (simple-base-string-p data)
-                       (data-vector-set (truly-the (simple-array base-char (*)) data) index (the base-char ,new-value))
+                       (data-vector-set (truly-the (simple-array base-char (*)) data) index (the* (base-char :silent-conflict t) ,new-value))
                        (data-vector-set (truly-the (simple-array character (*)) data) index (the character ,new-value)))
                   `(data-vector-set data index ,new-value))
              ,truly-new-value))))))
diff --git a/tests/array.pure.lisp b/tests/array.pure.lisp
index 27d8b3309..de550a526 100644
--- a/tests/array.pure.lisp
+++ b/tests/array.pure.lisp
@@ -1166,3 +1166,9 @@
    (lambda (x n)
      (aref (if n (the string n) #(1 2)) x))
    (or (integer 1 2) character)))
+
+#+sb-unicode
+(with-test (:name :char-base-char-warning)
+  (checked-compile
+   `(lambda (s)
+      (setf (char s 0) (code-char 233)))))
diff --git a/tests/utf-8.impure.lisp b/tests/utf-8.impure.lisp
index 6ffe631bc..0f1023f67 100644
--- a/tests/utf-8.impure.lisp
+++ b/tests/utf-8.impure.lisp
@@ -334,6 +334,7 @@
                    (error "~s" vector))))))
       (free-protected-array string))))
 
+#+(or arm64 x86-64)
 (with-test (:name :character-string-to-utf8)
   (flet ((run-test (string obuf vector)
            (loop repeat (* 256 #+slow 10)