diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 9757d7c..c7db981 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -5664,7 +5664,8 @@
 		match = FALSE;
 		break;
 	    }
-	    len2 += MB_CHAR2LEN(c2);
+	    len2 += enc_utf8 ? utf_ptr2len(rex.line + col + len2)
+							     : MB_CHAR2LEN(c2);
 	}
 	if (match
 		// check that no composing char follows
diff --git a/src/testdir/test_regexp_utf8.vim b/src/testdir/test_regexp_utf8.vim
index 9f0ffb9..044aeff 100644
--- a/src/testdir/test_regexp_utf8.vim
+++ b/src/testdir/test_regexp_utf8.vim
@@ -558,4 +558,12 @@
   bwipe!
 endfunc
 
+func Test_match_invalid_byte()
+  call writefile(0z630a.765d30aa0a.2e0a.790a.4030, 'Xinvalid')
+  new
+  source Xinvalid
+  bwipe!
+  call delete('Xinvalid')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 54533dc..0eb6899 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3409,
+/**/
     3408,
 /**/
     3407,