diff --git a/inc/adr68k.h b/inc/adr68k.h
index 9799780..42cae9c 100644
--- a/inc/adr68k.h
+++ b/inc/adr68k.h
@@ -63,8 +63,8 @@ static inline DLword StackOffsetFromNative(void *SAddr)
 {
   /* Stack offsets are expressed as an offset in DLwords from the stack base */
   ptrdiff_t hoffset = (DLword *)SAddr - Stackspace;
-  if (hoffset > 0xffff) {
-    printf("Stack offset is too large: 0x%tx\n", hoffset);
+  if (hoffset > 0xffff || hoffset < 0) {
+    printf("Stack offset is out of range: 0x%tx\n", hoffset);
   }
   return (DLword)hoffset;
 }
diff --git a/inc/return.h b/inc/return.h
index 90749fb..e493032 100644
--- a/inc/return.h
+++ b/inc/return.h
@@ -37,7 +37,7 @@
 #define FastRetCALL							\
   do {									\
     /* Get IVar from Returnee's IVAR offset slot(BF) */ 			\
-    IVar = NativeAligned2FromLAddr(STK_OFFSET | GETWORD((DLword *)CURRENTFX -1)); \
+    IVar = NativeAligned2FromStackOffset(GETWORD((DLword *)CURRENTFX - 1)); \
     /* Get FuncObj from Returnee's FNHEAD slot in FX */ 			\
     FuncObj = (struct fnhead *)NativeAligned4FromLAddr(FX_FNHEADER);	        \
     /* Get PC from Returnee's pc slot in FX */ 				\
@@ -47,7 +47,7 @@
 #define FastRetCALL							\
   do {									\
     /* Get IVar from Returnee's IVAR offset slot(BF) */ 			\
-    IVar = NativeAligned2FromLAddr(STK_OFFSET | GETWORD((DLword *)CURRENTFX -1)); \
+    IVar = NativeAligned2FromStackOffset(GETWORD((DLword *)CURRENTFX - 1)); \
     /* Get FuncObj from Returnee's FNHEAD slot in FX */ 			\
     FuncObj = (struct fnhead *)NativeAligned4FromLAddr(FX_FNHEADER);	        \
     /* Get PC from Returnee's pc slot in FX */ 				\
diff --git a/inc/stack.h b/inc/stack.h
index f93be91..721c15d 100644
--- a/inc/stack.h
+++ b/inc/stack.h
@@ -79,22 +79,22 @@ typedef struct fnhead {
 } FNHEAD;
 
 typedef struct frameex1 {
-  unsigned flags : 3;
-  unsigned fast : 1;
-  unsigned nil2 : 1; /* not used, prev: This frame treats N-func */
-  unsigned incall : 1;
-  unsigned validnametable : 1;
+  unsigned short flags : 3;
+  unsigned short fast : 1;
+  unsigned short nil2 : 1; /* not used, prev: This frame treats N-func */
+  unsigned short incall : 1;
+  unsigned short validnametable : 1;
   /* 0: look for FunctionHeader
      1: look for NameTable on this FrameEx */
-  unsigned nopush : 1;
-  unsigned usecount : 8;
+  unsigned short nopush : 1;
+  unsigned short usecount : 8;
   DLword alink; /* alink pointer (Low addr) */
 #ifdef BIGVM
   LispPTR fnheader; /* pointer to FunctionHeader (Hi2 addr) */
 #else
   DLword lofnheader;        /* pointer to FunctionHeader (Low addr) */
-  unsigned hi1fnheader : 8; /* pointer to FunctionHeader (Hi1 addr) */
-  unsigned hi2fnheader : 8; /* pointer to FunctionHeader (Hi2 addr) */
+  unsigned short hi1fnheader : 8; /* pointer to FunctionHeader (Hi1 addr) */
+  unsigned short hi2fnheader : 8; /* pointer to FunctionHeader (Hi2 addr) */
 #endif /* BIGVM */
   DLword nextblock; /* pointer to FreeStackBlock */
   DLword pc;        /* Program counter */
@@ -102,23 +102,23 @@ typedef struct frameex1 {
   LispPTR nametable; /* ptr to NameTable of this FrameEx (Hi2 addr) */
 #else
   DLword lonametable;        /* ptr to NameTable of this FrameEx (Low addr) */
-  unsigned hi1nametable : 8; /* ptr to NameTable of this FrameEx (Hi1 addr) */
-  unsigned hi2nametable : 8; /* ptr to NameTable of this FrameEx (Hi2 addr) */
+  unsigned short hi1nametable : 8; /* ptr to NameTable of this FrameEx (Hi1 addr) */
+  unsigned short hi2nametable : 8; /* ptr to NameTable of this FrameEx (Hi2 addr) */
 #endif /* BIGVM */
   DLword blink; /* blink pointer (Low addr) */
   DLword clink; /* clink pointer (Low addr) */
 } FX;
 
 typedef struct frameex2 {
-  unsigned flags : 3;
-  unsigned fast : 1;
-  unsigned nil2 : 1; /* not used, prev: This frame treats N-func */
-  unsigned incall : 1;
-  unsigned validnametable : 1;
+  unsigned short flags : 3;
+  unsigned short fast : 1;
+  unsigned short nil2 : 1; /* not used, prev: This frame treats N-func */
+  unsigned short incall : 1;
+  unsigned short validnametable : 1;
   /* 0: look for FunctionHeader
      1: look for NameTable on this FrameEx */
-  unsigned nopush : 1;
-  unsigned usecount : 8;
+  unsigned short nopush : 1;
+  unsigned short usecount : 8;
   DLword alink;      /* alink pointer (Low addr) */
   LispPTR fnheader;  /* pointer to FunctionHeader */
   DLword nextblock;  /* pointer to FreeStackBlock */
@@ -135,11 +135,11 @@ typedef struct fxblock {
 } FXBLOCK;
 
 typedef struct basic_frame {
-  unsigned flags : 3;
-  unsigned nil : 3;
-  unsigned residual : 1;
-  unsigned padding : 1;
-  unsigned usecnt : 8;
+  unsigned short flags : 3;
+  unsigned short nil : 3;
+  unsigned short residual : 1;
+  unsigned short padding : 1;
+  unsigned short usecnt : 8;
   DLword ivar; /* stk offset of IVARs for this frame ?? */
 
 } Bframe;
@@ -185,33 +185,33 @@ typedef struct fnhead {
   unsigned nil3 : 2;       /* not used */
   unsigned nil2 : 2;       /* not used */
 #endif /* BIGVM */
-  unsigned argtype : 2;     /* ?? */
-  unsigned byteswapped : 1; /* code was reswapped.	*/
-  unsigned nil4 : 1;        /* not used, prev: native translated? */
-  unsigned fvaroffset : 8;
+  unsigned short argtype : 2;     /* ?? */
+  unsigned short byteswapped : 1; /* code was reswapped.	*/
+  unsigned short nil4 : 1;        /* not used, prev: native translated? */
+  unsigned short fvaroffset : 8;
   /* DLword offset from head of NameTable */
-  unsigned nlocals : 8; /* ?? */
+  unsigned short nlocals : 8; /* ?? */
   DLword ntsize;        /* size of NameTable */
                         /* NameTable of variable length is following with this structure. */
 } FNHEAD;
 
 typedef struct frameex1 {
   DLword alink; /* alink pointer (Low addr) */
-  unsigned usecount : 8;
-  unsigned nopush : 1;
-  unsigned validnametable : 1;
+  unsigned short usecount : 8;
+  unsigned short nopush : 1;
+  unsigned short validnametable : 1;
   /* 0: look for FunctionHeader
      1: look for NameTable on this FrameEx */
-  unsigned incall : 1;
-  unsigned nil2 : 1; /* not used, prev: This frame treats N-func */
-  unsigned fast : 1;
-  unsigned flags : 3; /* hi word */
+  unsigned short incall : 1;
+  unsigned short nil2 : 1; /* not used, prev: This frame treats N-func */
+  unsigned short fast : 1;
+  unsigned short flags : 3; /* hi word */
 
 #ifdef BIGVM
   LispPTR fnheader; /* pointer to FunctionHeader (Hi2 addr) */
 #else
-  unsigned hi2fnheader : 8; /* pointer to FunctionHeader (Hi2 addr) */
-  unsigned hi1fnheader : 8; /* pointer to FunctionHeader (Hi1 addr) */
+  unsigned short hi2fnheader : 8; /* pointer to FunctionHeader (Hi2 addr) */
+  unsigned short hi1fnheader : 8; /* pointer to FunctionHeader (Hi1 addr) */
   DLword lofnheader;        /* pointer to FunctionHeader (Low addr) */
 #endif /* BIGVM */
 
@@ -221,8 +221,8 @@ typedef struct frameex1 {
 #ifdef BIGVM
   LispPTR nametable; /* pointer to NameTable of this FX (Hi2 addr) */
 #else
-  unsigned hi2nametable : 8; /* pointer to NameTable of this FX (Hi2 addr) */
-  unsigned hi1nametable : 8; /* pointer to NameTable of this FX (Hi1 addr) */
+  unsigned short hi2nametable : 8; /* pointer to NameTable of this FX (Hi2 addr) */
+  unsigned short hi1nametable : 8; /* pointer to NameTable of this FX (Hi1 addr) */
   DLword lonametable;        /* pointer to NameTable of this FX (Low addr) */
 #endif /* BIGVM */
 
@@ -232,15 +232,15 @@ typedef struct frameex1 {
 
 typedef struct frameex2 {
   DLword alink; /* alink pointer (Low addr) */
-  unsigned usecount : 8;
-  unsigned nopush : 1;
-  unsigned validnametable : 1;
+  unsigned short usecount : 8;
+  unsigned short nopush : 1;
+  unsigned short validnametable : 1;
   /* 0: look for FunctionHeader
      1: look for NameTable on this FrameEx */
-  unsigned incall : 1;
-  unsigned nil2 : 1; /* not used, prev: This frame treats N-func */
-  unsigned fast : 1;
-  unsigned flags : 3;
+  unsigned short incall : 1;
+  unsigned short nil2 : 1; /* not used, prev: This frame treats N-func */
+  unsigned short fast : 1;
+  unsigned short flags : 3;
 
   LispPTR fnheader; /* pointer to FunctionHeader (swapped) */
 
@@ -261,11 +261,11 @@ typedef struct fxblock {
 
 typedef struct basic_frame {
   DLword ivar;
-  unsigned usecnt : 8;
-  unsigned padding : 1;
-  unsigned residual : 1;
-  unsigned nil : 3;
-  unsigned flags : 3;
+  unsigned short usecnt : 8;
+  unsigned short padding : 1;
+  unsigned short residual : 1;
+  unsigned short nil : 3;
+  unsigned short flags : 3;
 
 } Bframe;
 
diff --git a/src/bbtsub.c b/src/bbtsub.c
index af07f14..e824b09 100644
--- a/src/bbtsub.c
+++ b/src/bbtsub.c
@@ -1664,7 +1664,7 @@ void ccfuncall(unsigned int atom_index, int argnum, int bytenum)
   CURRENTFX->nextblock = (LAddrFromNative(CurrentStackPTR) & 0x0ffff) - (argnum << 1) + 4 /* +3  */;
 
   /* Setup IVar */ /* XXX: is it really only 2-byte aligned? */
-  IVar = NativeAligned2FromLAddr((((LispPTR)(CURRENTFX->nextblock)) | STK_OFFSET));
+  IVar = NativeAligned2FromStackOffset(CURRENTFX->nextblock);
 
   /* Set PC to the Next Instruction and save into FX */
   CURRENTFX->pc = ((UNSIGNED)PC - (UNSIGNED)FuncObj) + bytenum;
diff --git a/src/dbgtool.c b/src/dbgtool.c
index 70ee8f4..3f0dad7 100644
--- a/src/dbgtool.c
+++ b/src/dbgtool.c
@@ -303,14 +303,14 @@ int sf(struct frameex1 *fx_addr68k) {
   if (((fx_addr68k)->alink & 1) == 0) { /* FAST */
     bf = (Bframe *)(((DLword *)fx_addr68k) - 2);
   } else { /* SLOW */
-    bf = (Bframe *)NativeAligned4FromLAddr(((fx_addr68k)->blink + STK_OFFSET));
+    bf = (Bframe *)NativeAligned4FromStackOffset((fx_addr68k)->blink);
   }
 
   /* Print IVARs */
   printf("IVAR -------\n");
   BT_morep;
 
-  ptr = NativeAligned2FromLAddr(STK_OFFSET + bf->ivar);
+  ptr = NativeAligned2FromStackOffset(bf->ivar);
   i = 0;
   while (ptr != (DLword *)bf) {
     ptrlo = ptr + 1;
@@ -475,7 +475,7 @@ int sf(struct frameex1 *fx_addr68k) {
       i++;
     }
     if (fx_addr68k->alink == 11) /* for contextsw */
-      next68k = (DLword *)NativeAligned2FromLAddr((fx_addr68k->nextblock + STK_OFFSET));
+      next68k = NativeAligned2FromStackOffset(fx_addr68k->nextblock);
 
     else
       next68k = CurrentStackPTR;
@@ -493,7 +493,7 @@ int sf(struct frameex1 *fx_addr68k) {
     return (-1);
   }
 
-  next68k = (DLword *)NativeAligned2FromLAddr((fx_addr68k->nextblock + STK_OFFSET));
+  next68k = NativeAligned2FromStackOffset(fx_addr68k->nextblock);
   ptr = (DLword *)(fx_addr68k + 1);
 
   i = 0;
diff --git a/src/findkey.c b/src/findkey.c
index 88d250a..f456f36 100644
--- a/src/findkey.c
+++ b/src/findkey.c
@@ -45,7 +45,7 @@ LispPTR N_OP_findkey(LispPTR tos, int byte) {
 #endif
 
   if (CURRENTFX->alink & 1) { /* slow case */
-    find_end = (DLword *)NativeAligned2FromLAddr(STK_OFFSET | (CURRENTFX->blink - 4));
+    find_end = NativeAligned2FromStackOffset(CURRENTFX->blink - 4);
   } else { /*  Fast cae */
     find_end = ((DLword *)CURRENTFX) - 2 - 4;
   }
diff --git a/src/loopsops.c b/src/loopsops.c
index 3544905..90e2c1e 100644
--- a/src/loopsops.c
+++ b/src/loopsops.c
@@ -26,7 +26,7 @@
 #include "gcarraydefs.h"   // for get_package_atom
 #include "gcdata.h"        // for FRPLPTR
 #include "lispemul.h"      // for LispPTR, state, CurrentStackPTR, NIL_PTR, NIL
-#include "lispmap.h"       // for S_POSITIVE, STK_OFFSET
+#include "lispmap.h"       // for S_POSITIVE
 #include "loopsopsdefs.h"  // for lcfuncall, LCFetchMethod, LCFetchMethodOrHelp
 #include "lspglob.h"
 #include "lsptypes.h"      // for GetDTD, GetTypeNumber, dtd, Listp, GETWORD
@@ -358,7 +358,7 @@ LispPTR lcfuncall(unsigned int atom_index, int argnum, int bytenum)
   CURRENTFX->nextblock = (LAddrFromNative(CurrentStackPTR) & 0x0ffff) - (argnum << 1) + 4 /* +3  */;
 
   /* Setup IVar */
-  IVar = NativeAligned2FromLAddr((((LispPTR)(CURRENTFX->nextblock)) | STK_OFFSET));
+  IVar = NativeAligned2FromStackOffset(CURRENTFX->nextblock);
 
   /* Set PC to the Next Instruction and save into FX */
   CURRENTFX->pc = ((UNSIGNED)PC - (UNSIGNED)FuncObj) + bytenum;
diff --git a/src/main.c b/src/main.c
index 4d23107..b6e05a8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -727,9 +727,9 @@ void start_lisp(void) {
   TopOfStack = 0;
   Error_Exit = 0;
 
-  PVar = (DLword *)NativeAligned2FromLAddr(STK_OFFSET | InterfacePage->currentfxp) + FRAMESIZE;
+  PVar = NativeAligned2FromStackOffset(InterfacePage->currentfxp) + FRAMESIZE;
 
-  freeptr = next68k = NativeAligned2FromLAddr(STK_OFFSET | CURRENTFX->nextblock);
+  freeptr = next68k = NativeAligned2FromStackOffset(CURRENTFX->nextblock);
 
   if (GETWORD(next68k) != STK_FSB_WORD) error("Starting Lisp: Next stack block isn't free!");
 
diff --git a/src/return.c b/src/return.c
index 0b8a23b..fe87cf6 100644
--- a/src/return.c
+++ b/src/return.c
@@ -129,7 +129,7 @@ void contextsw(DLword fxnum, DLword bytenum, DLword flags)
 
   Midpunt(fxnum); /* exchanging FX */
 
-  next68k = (DLword *)NativeAligned2FromLAddr(STK_OFFSET | CURRENTFX->nextblock);
+  next68k = NativeAligned2FromStackOffset(CURRENTFX->nextblock);
 
   if (GETWORD(next68k) != STK_FSB_WORD) error("contextsw(): MP9316");
   freeptr = next68k;
diff --git a/src/testtool.c b/src/testtool.c
index 1f49fd0..bf6b8a7 100644
--- a/src/testtool.c
+++ b/src/testtool.c
@@ -57,7 +57,7 @@
 #include "gcarraydefs.h"   // for aref1
 #include "kprintdefs.h"    // for print, prindatum
 #include "lispemul.h"      // for DLword, LispPTR, DLbyte, state, T, ConsCell
-#include "lispmap.h"       // for STK_OFFSET, ATOMS_HI
+#include "lispmap.h"       // for ATOMS_HI
 #include "lspglob.h"       // for Package_from_Index_word, Stackspace
 #include "lsptypes.h"      // for GETWORD, dtd, GETBYTE, NEWSTRINGP, GetType...
 #include "mkatomdefs.h"    // for compare_chars, make_atom
@@ -852,7 +852,7 @@ void dump_bf(Bframe *bf) {
 
   if (BFRAMEPTR(bf)->residual) { goto printflags; }
 
-  ptr = NativeAligned2FromLAddr(STK_OFFSET + bf->ivar);
+  ptr = NativeAligned2FromStackOffset(bf->ivar);
   if ((((DLword *)bf - ptr) > 512) || (((UNSIGNED)ptr & 1) != 0)) {
     printf("\nInvalid basic frame");
     return;
@@ -910,7 +910,7 @@ void dump_fx(struct frameex1 *fx_addr68k) {
 
   /* should pay attention to the name table like RAID does */
 
-  next68k = (DLword *)NativeAligned2FromLAddr((fx_addr68k->nextblock + STK_OFFSET));
+  next68k = NativeAligned2FromStackOffset(fx_addr68k->nextblock);
   if (fx_addr68k == CURRENTFX) { next68k = CurrentStackPTR + 2; }
 
   if ((next68k < ptr) || (((UNSIGNED)next68k & 1) != 0)) {
@@ -937,7 +937,7 @@ void dump_stackframe(struct frameex1 *fx_addr68k) {
   if ((fx_addr68k->alink & 1) == 0) { /* FAST */
     bf = (Bframe *)(((DLword *)fx_addr68k) - 2);
   } else { /* SLOW */
-    bf = (Bframe *)NativeAligned4FromLAddr((fx_addr68k->blink + STK_OFFSET));
+    bf = (Bframe *)NativeAligned4FromStackOffset(fx_addr68k->blink);
   }
   dump_bf(bf);
   dump_fx((struct frameex1 *)fx_addr68k);
@@ -1104,12 +1104,12 @@ void all_stack_dump(DLword start, DLword end, DLword silent)
   if (start == 0)
     start68k = Stackspace + InterfacePage->stackbase;
   else
-    start68k = NativeAligned2FromLAddr(STK_OFFSET | start);
+    start68k = NativeAligned2FromStackOffset(start);
 
   if (end == 0)
     end68k = Stackspace + InterfacePage->endofstack;
   else
-    end68k = NativeAligned2FromLAddr(STK_OFFSET | end);
+    end68k = NativeAligned2FromStackOffset(end);
 
   stkptr = (STKH *)start68k;
 
@@ -1156,7 +1156,7 @@ void all_stack_dump(DLword start, DLword end, DLword silent)
           printf(" <-***current***");
           size = EndSTKP - (DLword *)stkptr;
         } else {
-          size = NativeAligned2FromLAddr(STK_OFFSET | ((FX *)stkptr)->nextblock) - (DLword *)stkptr;
+          size = NativeAligned2FromStackOffset(((FX *)stkptr)->nextblock) - (DLword *)stkptr;
         }
         goto checksize;
       default:
diff --git a/src/ufn.c b/src/ufn.c
index 3f64be2..93eeff7 100644
--- a/src/ufn.c
+++ b/src/ufn.c
@@ -107,7 +107,7 @@ void ufn(DLword bytecode)
       (LAddrFromNative(CurrentStackPTR) & 0x0ffff) - (entry68k->arg_num << 1) + 2 /** +1 **/;
 
   /* Setup IVar */
-  IVar = NativeAligned2FromLAddr((((LispPTR)(CURRENTFX->nextblock)) | STK_OFFSET));
+  IVar = NativeAligned2FromStackOffset(CURRENTFX->nextblock);
 
 #ifdef LISPTRACE
   print(entry68k->atom_name);