diff --git a/string.c b/string.c
index b303b56d89..f0ce9b1109 100644
--- a/string.c
+++ b/string.c
@@ -6075,15 +6075,17 @@ rb_str_count(int argc, VALUE *argv, VALUE str)
     rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
     for (i=0; i<argc; i++) {
 	VALUE tstr = argv[i];
-	const unsigned char *utstr;
+	const char *ptstr;
 
 	StringValue(tstr);
 	enc = rb_enc_check(str, tstr);
 	if (argc == 1 && RSTRING_LEN(tstr) == 1 && rb_enc_asciicompat(enc) &&
-	    (utstr = (const OnigUChar *)RSTRING_PTR(tstr), ONIGENC_IS_ALLOWED_REVERSE_MATCH(enc, utstr, utstr+1)) &&
+	    (ptstr = RSTRING_PTR(tstr),
+	     ONIGENC_IS_ALLOWED_REVERSE_MATCH(enc, (const unsigned char *)ptstr, (const unsigned char *)ptstr+1)) &&
 	    !is_broken_string(str)) {
 	    int n = 0;
-	    unsigned char c = utstr[0];
+	    int clen;
+	    unsigned char c = rb_enc_codepoint_len(ptstr, ptstr+1, &clen, enc);
 
 	    s = RSTRING_PTR(str);
 	    if (!s || RSTRING_LEN(str) == 0) return INT2FIX(0);
diff --git a/test/ruby/test_m17n_comb.rb b/test/ruby/test_m17n_comb.rb
index 12aa4d539d..b7efd030fe 100644
--- a/test/ruby/test_m17n_comb.rb
+++ b/test/ruby/test_m17n_comb.rb
@@ -88,7 +88,7 @@ class TestM17NComb < Test::Unit::TestCase
     r
   end
 
-  def assert_enccall(recv, meth, *args, &block)
+  def encdumpcall(recv, meth, *args, &block)
     desc = ''
     if String === recv
       desc << encdump(recv)
@@ -111,6 +111,11 @@ class TestM17NComb < Test::Unit::TestCase
     if block
       desc << ' {}'
     end
+    desc
+  end
+
+  def assert_enccall(recv, meth, *args, &block)
+    desc = encdumpcall(recv, meth, *args, &block)
     result = nil
     assert_nothing_raised(desc) {
       result = recv.send(meth, *args, &block)
@@ -710,12 +715,13 @@ class TestM17NComb < Test::Unit::TestCase
 
   def test_str_count
     combination(STRINGS, STRINGS) {|s1, s2|
+      desc = proc {encdumpcall(s1, :count, s2)}
       if !s1.valid_encoding? || !s2.valid_encoding?
-        assert_raise(ArgumentError, Encoding::CompatibilityError) { s1.count(s2) }
+        assert_raise(ArgumentError, Encoding::CompatibilityError, desc) { s1.count(s2) }
         next
       end
       if !s1.ascii_only? && !s2.ascii_only? && s1.encoding != s2.encoding
-        assert_raise(Encoding::CompatibilityError) { s1.count(s2) }
+        assert_raise(Encoding::CompatibilityError, desc) { s1.count(s2) }
         next
       end
       n = enccall(s1, :count, s2)