diff --git a/src/nvim/regexp.c b/src/nvim/regexp.c
index 3b63c6ec8f..5074e3a8d5 100644
--- a/src/nvim/regexp.c
+++ b/src/nvim/regexp.c
@@ -1759,7 +1759,7 @@ static int cstrncmp(char *s1, char *s2, int *n)
     int n1 = *n;
     // count the number of characters for byte-length of s1
     while (n1 > 0 && *p != NUL) {
-      n1 -= utfc_ptr2len(s1);
+      n1 -= utfc_ptr2len(p);
       MB_PTR_ADV(p);
       n2++;
     }
diff --git a/test/old/testdir/test_regexp_utf8.vim b/test/old/testdir/test_regexp_utf8.vim
index f5ec0b77d2..272d3d535e 100644
--- a/test/old/testdir/test_regexp_utf8.vim
+++ b/test/old/testdir/test_regexp_utf8.vim
@@ -363,6 +363,12 @@ func Run_regexp_ignore_case()
   call assert_equal('iIx', substitute('iIİ', '\c\(\%u0130\)', 'x', 'g'))
   call assert_equal('iIx', substitute('iIİ', '\c\([\u0130]\)', 'x', 'g'))
   call assert_equal('iIx', substitute('iIİ', '\c\([\u012f-\u0131]\)', 'x', 'g'))
+
+  " Ignoring case in a literal string that starts with a character longer
+  " than a following one must still match.
+  call assert_equal('Über', matchstr('Überraschung', '\cüber'))
+  call assert_equal('Ünder', matchstr('Ünderdog', '\cünder'))
+  call assert_equal('αaaa', matchstr('αaaaa', '\cαaaa'))
 endfunc
 
 func Test_regexp_ignore_case()