diff --git a/startup.4th b/startup.4th
index eb40c71..86fe31a 100644
--- a/startup.4th
+++ b/startup.4th
@@ -1451,9 +1451,16 @@ VARIABLE TOTAL
 : ENDSTRUCT ( align offset "<spaces?>name" -- )
    OVER ALIGNED-TO 2CONSTANT ;
 
+\ Accessors for type descriptors
+: %SIZEOF ( align size -- size ) NIP ;
+: %ALIGNOF ( align size -- align ) DROP ;
+
 \ Reserve data or heap space for a data structure given alignment and size
-: %ALLOT ( align bytes -- a-addr ) SWAP ALIGN-TO ALLOT ;
-: %ALLOCATE ( align bytes -- a-addr ) NIP ALLOCATE ;
+\ It is assumed that ALLOCATE (but not ALLOT) returns an address suitably
+\ aligned for any primitive data type; %ALLOCATE is not suitable for data
+\ structures with unusually high alignment requirements
+: %ALLOT ( align bytes -- a-addr ) SWAP ALIGN-TO HERE SWAP ALLOT ;
+: %ALLOCATE ( align bytes -- a-addr ) %SIZEOF ALLOCATE ;
 
 >>SYSTEM
 
@@ -1821,7 +1828,7 @@ ENDSTRUCT termios%
 
 >>SYSTEM
 
-CREATE SCRATCH-TERMIOS termios% %ALLOT
+termios% %ALLOT CONSTANT SCRATCH-TERMIOS
 
 >>FORTH