diff --git a/library/dialect/swi/fli/swi.c b/library/dialect/swi/fli/swi.c
index 5946702b4..c7266cefe 100755
--- a/library/dialect/swi/fli/swi.c
+++ b/library/dialect/swi/fli/swi.c
@@ -50,12 +50,12 @@
 extern X_API Int YAP_PLArityOfSWIFunctor(functor_t at);
 
 X_API Int
-YAP_PLArityOfSWIFunctor(functor_t at) {
-  if (IsAtomTerm(at))
+YAP_PLArityOfSWIFunctor(functor_t f) {
+  if (IsAtomTerm(f))
     return 0;
-  if ((CELL)(at) & 2)
-    return ArityOfFunctor(SWI_Functors[((CELL)at)/4]);
-  return ArityOfFunctor((Functor)at);
+  if ((CELL)f < N_SWI_FUNCTORS*(LowTagBits+1))
+    return ArityOfFunctor(SWI_Functors[(CELL)f/(LowTagBits+1)]);
+  return ArityOfFunctor((Functor)f);
 }
 
 void
@@ -64,10 +64,10 @@ Yap_InitSWIHash(void)
   int i, j;
   memset(SWI_ReverseHash, 0, N_SWI_HASH*sizeof(swi_rev_hash));
   for (i=0; i < N_SWI_ATOMS; i++) {
-    add_to_hash(i*2+1, (ADDR)SWI_Atoms[i]);
+    add_to_hash(i, (ADDR)SWI_Atoms[i]);
   }
   for (j=0; j < N_SWI_FUNCTORS; j++) {
-    add_to_hash((((CELL)(j))*4+2), (ADDR)SWI_Functors[j]);
+    add_to_hash(j, (ADDR)SWI_Functors[j]);
   }
 }
 
diff --git a/library/dialect/swi/fli/swi.h b/library/dialect/swi/fli/swi.h
index 3032aece8..9fd1a3c4c 100644
--- a/library/dialect/swi/fli/swi.h
+++ b/library/dialect/swi/fli/swi.h
@@ -83,15 +83,15 @@ AtomToSWIAtom(Atom at)
 {
   atom_t ats;
   if ((ats = in_hash((ADDR)at)))
-    return ats;
+    return (atom_t)((CELL)at*(LowTagBits+1));
   return (atom_t)at;
 }
 
 static inline Atom
 SWIAtomToAtom(atom_t at)
 {
-  if ((CELL)at & 1)
-    return SWI_Atoms[at>>1];
+  if ((CELL)at < N_SWI_ATOMS*(LowTagBits+1))
+    return SWI_Atoms[((CELL)at)/(LowTagBits+1)];
   return (Atom)at;
 }
 
@@ -110,17 +110,17 @@ FunctorToSWIFunctor(Functor at)
 {
   atom_t ats;
   if ((ats = in_hash((ADDR)at)))
-    return (functor_t)ats;
+    return (functor_t)((CELL)at*(LowTagBits+1));
   return (functor_t)at;
 }
 
 static inline Functor
-SWIFunctorToFunctor(functor_t at)
+SWIFunctorToFunctor(functor_t f)
 {
-  if (IsAtomTerm(at))
-    return (Functor)at;
-  if ((CELL)(at) & 2)
-    return SWI_Functors[((CELL)at)/4];
-  return (Functor)at;
+  if (IsAtomTerm(f))
+    return (Functor)f;
+  if ((CELL)f < N_SWI_FUNCTORS*(LowTagBits+1))
+    return SWI_Functors[(CELL)f/(LowTagBits+1)];
+  return (Functor)f;
 }