diff --git a/ext/syck/implicit.c b/ext/syck/implicit.c
index 6911e61..734f53f 100644
--- a/ext/syck/implicit.c
+++ b/ext/syck/implicit.c
@@ -11,7 +11,7 @@
 #include "ruby/ruby.h"
 #include "syck.h"
 
-#define YYCTYPE     char
+#define YYCTYPE     unsigned char
 #define YYCURSOR    cursor
 #define YYMARKER    marker
 #define YYLIMIT     limit
diff --git a/test/test_boolean.rb b/test/test_boolean.rb
index edaffa6..bde17ed 100644
--- a/test/test_boolean.rb
+++ b/test/test_boolean.rb
@@ -32,5 +32,17 @@ def test_n
       assert_equal "n", Syck.load("--- n")
       assert_equal "N", Syck.load("--- N")
     end
+
+    ###
+    # https://github.com/ruby/syck/issues/22
+    # A boolean-like prefix followed by a non-ASCII byte must not be
+    # matched as a boolean
+    def test_bool_prefix_with_non_ascii
+      assert_equal "Noémie", Syck.load("--- Noémie")
+      assert_equal ["Noémie"], Syck.load("--- [Noémie]")
+      assert_equal "Yeså", Syck.load("--- Yeså")
+      assert_equal "trueé", Syck.load("--- trueé")
+      assert_equal "nullé", Syck.load("--- nullé")
+    end
   end
 end