diff --git a/core/io/encodings/utf8/utf8-tests.factor b/core/io/encodings/utf8/utf8-tests.factor
index efebe7bd25..6d785ce9c3 100644
--- a/core/io/encodings/utf8/utf8-tests.factor
+++ b/core/io/encodings/utf8/utf8-tests.factor
@@ -8,19 +8,19 @@ IN: io.encodings.utf8.tests
 : encode-utf8-w/stream ( array -- newarray )
     >string utf8 encode >array ;
 
-[ { CHAR: replacement-character } ] [ { BIN: 11110101 BIN: 10111111 BIN: 10000000 BIN: 11111111 } decode-utf8-w/stream ] unit-test
+[ { CHAR: replacement-character } ] [ { BIN: 11110,101 BIN: 10,111111 BIN: 10,000000 BIN: 11111111 } decode-utf8-w/stream ] unit-test
 
-[ { BIN: 101111111000000111111 } ] [ { BIN: 11110101 BIN: 10111111 BIN: 10000000 BIN: 10111111 } decode-utf8-w/stream ] unit-test
+[ { BIN: 101111111000000111111 } ] [ { BIN: 11110,101 BIN: 10,111111 BIN: 10,000000 BIN: 10,111111 } decode-utf8-w/stream ] unit-test
 
 [ "x" ] [ "x" decode-utf8-w/stream >string ] unit-test
 
-[ { BIN: 11111000000 } ] [ { BIN: 11011111 BIN: 10000000 } decode-utf8-w/stream >array ] unit-test
+[ { BIN: 11111000000 } ] [ { BIN: 110,11111 BIN: 10,000000 } decode-utf8-w/stream >array ] unit-test
 
 [ { CHAR: replacement-character } ] [ { BIN: 10000000 } decode-utf8-w/stream ] unit-test
 
-[ { BIN: 1111000000111111 } ] [ { BIN: 11101111 BIN: 10000000 BIN: 10111111 } decode-utf8-w/stream >array ] unit-test
+[ { BIN: 1111000000111111 } ] [ { BIN: 1110,1111 BIN: 10,000000 BIN: 10,111111 } decode-utf8-w/stream >array ] unit-test
 
-[ { BIN: 11110101 BIN: 10111111 BIN: 10000000 BIN: 10111111 BIN: 11101111 BIN: 10000000 BIN: 10111111 BIN: 11011111 BIN: 10000000 CHAR: x } ]
+[ { BIN: 11110,101 BIN: 10,111111 BIN: 10,000000 BIN: 10,111111 BIN: 1110,1111 BIN: 10,000000 BIN: 10,111111 BIN: 110,11111 BIN: 10,000000 CHAR: x } ]
 [ { BIN: 101111111000000111111 BIN: 1111000000111111 BIN: 11111000000 CHAR: x } encode-utf8-w/stream ] unit-test
 
 [ 3 ] [ 1 "日本語" >utf8-index ] unit-test
@@ -29,3 +29,15 @@ IN: io.encodings.utf8.tests
 [ 3 ] [ 2 "lápis" >utf8-index ] unit-test
 
 [ V{ } ] [ 100000 iota [ [ code-point-length ] [ 1string utf8 encode length ] bi = not ] filter ] unit-test
+
+[ { CHAR: replacement-character } ] [ { BIN: 110,00000 BIN: 10,000000 } decode-utf8-w/stream ] unit-test
+[ { CHAR: replacement-character } ] [ { BIN: 110,00001 BIN: 10,111111 } decode-utf8-w/stream ] unit-test
+[ { HEX: 80 } ] [ { BIN: 110,00010 BIN: 10,000000 } decode-utf8-w/stream ] unit-test
+
+[ { CHAR: replacement-character } ] [ { BIN: 1110,0000 BIN: 10,000000 BIN: 10,000000 } decode-utf8-w/stream ] unit-test
+[ { CHAR: replacement-character } ] [ { BIN: 1110,0000 BIN: 10,011111 BIN: 10,111111 } decode-utf8-w/stream ] unit-test
+[ { HEX: 800 } ] [ { BIN: 1110,0000 BIN: 10,100000 BIN: 10,000000 } decode-utf8-w/stream ] unit-test
+
+[ { CHAR: replacement-character } ] [ { BIN: 11110,000 BIN: 10,000000 BIN: 10,000000 BIN: 10,000000 } decode-utf8-w/stream ] unit-test
+[ { CHAR: replacement-character } ] [ { BIN: 11110,000 BIN: 10,001111 BIN: 10,111111 BIN: 10,111111 } decode-utf8-w/stream ] unit-test
+[ { HEX: 10000 } ] [ { BIN: 11110,000 BIN: 10,010000 BIN: 10,000000 BIN: 10,000000 } decode-utf8-w/stream ] unit-test
diff --git a/core/io/encodings/utf8/utf8.factor b/core/io/encodings/utf8/utf8.factor
index c78a86c072..b6c89a6983 100644
--- a/core/io/encodings/utf8/utf8.factor
+++ b/core/io/encodings/utf8/utf8.factor
@@ -19,14 +19,20 @@ SINGLETON: utf8
     [ swap 6 shift swap BIN: 111111 bitand bitor ]
     [ 2drop replacement-char ] if ; inline
 
+: minimum-code-point ( char minimum -- char )
+    over > [ drop replacement-char ] when ; 
+
 : double ( stream byte -- stream char )
-    BIN: 11111 bitand append-nums ; inline
+    BIN: 11111 bitand append-nums
+    HEX: 80 minimum-code-point ; inline
 
 : triple ( stream byte -- stream char )
-    BIN: 1111 bitand append-nums append-nums ; inline
+    BIN: 1111 bitand append-nums append-nums
+    HEX: 800 minimum-code-point ; inline
 
 : quadruple ( stream byte -- stream char )
-    BIN: 111 bitand append-nums append-nums append-nums ; inline
+    BIN: 111 bitand append-nums append-nums append-nums
+    HEX: 10000 minimum-code-point ; inline
 
 : begin-utf8 ( stream byte -- stream char )
     {