diff --git a/ChangeLog b/ChangeLog
index d063d0904a..fd54c360fe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -53,6 +53,11 @@ Wed May 20 18:34:30 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* enumerator.c (inspect_enumerator): should use long.
 
+Wed May 20 09:18:44 2009  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* string.c (rb_str_count): optimized for 1byte string count by
+	  avoiding tr_setup_table().
+
 Wed May 20 06:25:29 2009  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* encoding.c (rb_enc_fast_mbclen): faster mbclen for strings known
diff --git a/string.c b/string.c
index 405500b1d2..b714864474 100644
--- a/string.c
+++ b/string.c
@@ -5380,19 +5380,31 @@ rb_str_count(int argc, VALUE *argv, VALUE str)
 	rb_raise(rb_eArgError, "wrong number of arguments");
     }
     for (i=0; i<argc; i++) {
-	VALUE s = argv[i];
+	VALUE tstr = argv[i];
+	unsigned char c;
 
-	StringValue(s);
-	enc = rb_enc_check(str, s);
-	tr_setup_table(s, table, i==0, &del, &nodel, enc);
+	StringValue(tstr);
+	enc = rb_enc_check(str, tstr);
+	if (argc == 1 && RSTRING_LEN(tstr) == 1 && rb_enc_asciicompat(enc) &&
+	    (c = RSTRING_PTR(tstr)[0]) < 0x80 && !is_broken_string(str)) {
+	    int n = 0;
+
+	    s = RSTRING_PTR(str);
+	    if (!s || RSTRING_LEN(str) == 0) return INT2FIX(0);
+	    send = RSTRING_END(str);
+	    while (s < send) {
+		if (*(unsigned char*)s++ == c) n++;
+	    }
+	    return INT2NUM(n);
+	}
+	tr_setup_table(tstr, table, i==0, &del, &nodel, enc);
     }
 
     s = RSTRING_PTR(str);
     if (!s || RSTRING_LEN(str) == 0) return INT2FIX(0);
     send = RSTRING_END(str);
-    i = 0;
     ascompat = rb_enc_asciicompat(enc);
-
+    i = 0;
     while (s < send) {
 	unsigned int c;
 	int clen;