diff --git a/basis/byte-arrays/hex/hex-docs.factor b/basis/byte-arrays/hex/hex-docs.factor
index 8a2b842fc9..c2cac8d584 100644
--- a/basis/byte-arrays/hex/hex-docs.factor
+++ b/basis/byte-arrays/hex/hex-docs.factor
@@ -5,4 +5,4 @@ USING: byte-arrays help.markup help.syntax ;
 
 HELP: HEX{
 { $syntax "HEX{ 0123 45 67 89abcdef }" }
-{ $description "Constructs a " { $link byte-array } " from data specified in hexadecimal format. Whitespace between the curly braces is ignored." } ;
+{ $description "Constructs a " { $link byte-array } " from data specified in hexadecimal format. Whitespace between the curly braces is ignored. There must be an even number of hex digits or an error is thrown." } ;
diff --git a/basis/byte-arrays/hex/hex-tests.factor b/basis/byte-arrays/hex/hex-tests.factor
new file mode 100644
index 0000000000..25f15405e9
--- /dev/null
+++ b/basis/byte-arrays/hex/hex-tests.factor
@@ -0,0 +1,11 @@
+! Copyright (C) 2011 Doug Coleman.
+! See http://factorcode.org/license.txt for BSD license.
+USING: tools.test byte-arrays.hex eval ;
+IN: byte-arrays.hex.tests
+
+[ B{ 16 0 8 0 } ] [ HEX{ 10 00 08 00 } ] unit-test
+[ B{ 255 255 15 255 255 255 } ] [ HEX{ ffff 0fff ffff } ] unit-test
+
+[ "HEX{ ffff fff ffff }" parse-string ] must-fail
+[ "HEX{ 10 00 08 0 }" parse-string ] must-fail
+[ "HEX{ 1 00 00 80 }" parse-string ] must-fail
diff --git a/basis/byte-arrays/hex/hex.factor b/basis/byte-arrays/hex/hex.factor
index ae9b9c8ba2..4912b0b98b 100644
--- a/basis/byte-arrays/hex/hex.factor
+++ b/basis/byte-arrays/hex/hex.factor
@@ -1,10 +1,14 @@
-! Copyright (C) 2009 Maxim Savchenko, Slava Pestov.
+! Copyright (C) 2009,2011 Maxim Savchenko, Slava Pestov, Doug Coleman.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: grouping lexer ascii parser sequences kernel math.parser ;
+USING: ascii grouping kernel math.parser sequences
+strings.parser lexer math ;
 IN: byte-arrays.hex
 
+ERROR: odd-length-hex-string string ;
+
 SYNTAX: HEX{
     "}" parse-tokens "" join
     [ blank? not ] filter
+    dup length even? [ odd-length-hex-string ] unless
     2 group [ hex> ] B{ } map-as
     suffix! ;