diff --git a/core/math/parser/parser-tests.factor b/core/math/parser/parser-tests.factor
index 9e3b3d21590..13e4514c436 100644
--- a/core/math/parser/parser-tests.factor
+++ b/core/math/parser/parser-tests.factor
@@ -480,6 +480,7 @@ unit-test
 
 { "deadbeef" } [ B{ 222 173 190 239 } bytes>hex-string ] unit-test
 { B{ 222 173 190 239 } } [ "deADbeEF" hex-string>bytes ] unit-test
+[ "0" hex-string>bytes ] [ invalid-hex-string-length? ] must-fail-with
 
 {
     B{ 49 46 53 53 69 43 48 53 }
diff --git a/core/math/parser/parser.factor b/core/math/parser/parser.factor
index 2e1d5a4b0f4..778c754981c 100644
--- a/core/math/parser/parser.factor
+++ b/core/math/parser/parser.factor
@@ -1019,8 +1019,10 @@ M: float >base
 
 : # ( n -- ) number>string % ; inline
 
+ERROR: invalid-hex-string-length n ;
+
 : hex-string>bytes ( hex-string -- bytes )
-    dup length 2/ <byte-array> [
+    dup length dup even? [ invalid-hex-string-length ] unless 2/ <byte-array> [
         [
             [ digit> ] 2dip over even? [
                 [ 16 * ] [ 2/ ] [ set-nth-unsafe ] tri*