diff --git a/string.c b/string.c
index 5eda835f4b..4c0fe87635 100644
--- a/string.c
+++ b/string.c
@@ -7987,7 +7987,14 @@ tr_trans(VALUE str, VALUE src, VALUE repl, int sflag)
         while (s < send) {
             int may_modify = 0;
 
-            c0 = c = rb_enc_codepoint_len((char *)s, (char *)send, &clen, e1);
+            int r = rb_enc_precise_mbclen((char *)s, (char *)send, e1);
+            if (!MBCLEN_CHARFOUND_P(r)) {
+                xfree(buf);
+                rb_raise(rb_eArgError, "invalid byte sequence in %s", rb_enc_name(e1));
+            }
+            clen = MBCLEN_CHARFOUND_LEN(r);
+            c0 = c = rb_enc_mbc_to_codepoint((char *)s, (char *)send, e1);
+
             tlen = enc == e1 ? clen : rb_enc_codelen(c, enc);
 
             s += clen;
@@ -8067,7 +8074,15 @@ tr_trans(VALUE str, VALUE src, VALUE repl, int sflag)
 
         while (s < send) {
             int may_modify = 0;
-            c0 = c = rb_enc_codepoint_len((char *)s, (char *)send, &clen, e1);
+
+            int r = rb_enc_precise_mbclen((char *)s, (char *)send, e1);
+            if (!MBCLEN_CHARFOUND_P(r)) {
+                xfree(buf);
+                rb_raise(rb_eArgError, "invalid byte sequence in %s", rb_enc_name(e1));
+            }
+            clen = MBCLEN_CHARFOUND_LEN(r);
+            c0 = c = rb_enc_mbc_to_codepoint((char *)s, (char *)send, e1);
+
             tlen = enc == e1 ? clen : rb_enc_codelen(c, enc);
 
             if (c < 256) {