diff --git a/core/math/parser/parser-tests.factor b/core/math/parser/parser-tests.factor
index 24ccd1aab8..017f208d79 100644
--- a/core/math/parser/parser-tests.factor
+++ b/core/math/parser/parser-tests.factor
@@ -318,6 +318,14 @@ unit-test
 {  -8 } [ "-0o10" string>number ] unit-test
 {  -2 } [ "-0b10" string>number ] unit-test
 
+{ 16 } [ "0X10" string>number ] unit-test
+{  8 } [ "0O10" string>number ] unit-test
+{  2 } [ "0B10" string>number ] unit-test
+
+{ -16 } [ "-0X10" string>number ] unit-test
+{  -8 } [ "-0O10" string>number ] unit-test
+{  -2 } [ "-0B10" string>number ] unit-test
+
 { f } [ "01a" string>number ] unit-test
 { f } [ "0x1g" string>number ] unit-test
 { f } [ "0o18" string>number ] unit-test
diff --git a/core/math/parser/parser.factor b/core/math/parser/parser.factor
index 5a683d921d..db8b42c2e4 100644
--- a/core/math/parser/parser.factor
+++ b/core/math/parser/parser.factor
@@ -306,11 +306,11 @@ DEFER: @neg-digit
 : with-radix-char ( i number-parse n radix-quot nonradix-quot -- n/f )
     [
         rot {
-            { CHAR: b [ drop  2 ->radix require-next-digit ] }
-            { CHAR: o [ drop  8 ->radix require-next-digit ] }
-            { CHAR: x [ drop 16 ->radix require-next-digit ] }
+            { [ dup "bB" member-eq? ] [ 2drop  2 ->radix require-next-digit ] }
+            { [ dup "oO" member-eq? ] [ 2drop  8 ->radix require-next-digit ] }
+            { [ dup "xX" member-eq? ] [ 2drop 16 ->radix require-next-digit ] }
             [ [ drop ] 2dip swap call ]
-        } case
+        } cond
     ] 2curry next-digit ; inline
 
 : @pos-first-digit ( i number-parse n char -- n/f )