diff --git a/moo/kernel/Magnitu.moo b/moo/kernel/Magnitu.moo
index 47ff68a..7cbea74 100644
--- a/moo/kernel/Magnitu.moo
+++ b/moo/kernel/Magnitu.moo
@@ -370,18 +370,23 @@ class(#limited) SmallInteger(Integer)
 	method(#primitive) asError.
 }
 
-class(#liword,#limited) LargeInteger(Integer)
+class(#limited,#immutable,#liword) LargeInteger(Integer)
 {
 }
 
-class(#liword,#immutable) LargePositiveInteger(LargeInteger)
+class(#limited,#immutable,#liword) LargePositiveInteger(LargeInteger)
 {
 	method abs { ^self }
 	method sign { ^1 }
 }
 
-class(#liword,#immutable) LargeNegativeInteger(LargeInteger)
+class(#limited,#immutable,#liword) LargeNegativeInteger(LargeInteger)
 {
 	method abs { ^self negated }
 	method sign { ^-1 }
 }
+
+class(#limited,#immutable) FixedPointDecimal(Number)
+{
+	var value, scale.
+}
diff --git a/moo/lib/gc.c b/moo/lib/gc.c
index 9116150..927e0d9 100644
--- a/moo/lib/gc.c
+++ b/moo/lib/gc.c
@@ -360,7 +360,7 @@ static kernel_class_info_t kernel_classes[] =
 
 	{ 20,
 	  { 'L','a','r','g','e','P','o','s','i','t','i','v','e','I','n','t','e','g','e','r' },
-	  0,
+	  MOO_CLASS_SELFSPEC_FLAG_LIMITED,
 	  0,
 	  0,
 	  MOO_CLASS_SPEC_FLAG_INDEXED | MOO_CLASS_SPEC_FLAG_IMMUTABLE,
@@ -369,7 +369,7 @@ static kernel_class_info_t kernel_classes[] =
 
 	{ 20,
 	  { 'L','a','r','g','e','N','e','g','a','t','i','v','e','I','n','t','e','g','e','r' },
-	  0,
+	  MOO_CLASS_SELFSPEC_FLAG_LIMITED,
 	  0,
 	  0,
 	  MOO_CLASS_SPEC_FLAG_INDEXED | MOO_CLASS_SPEC_FLAG_IMMUTABLE,
@@ -381,7 +381,7 @@ static kernel_class_info_t kernel_classes[] =
 	  MOO_CLASS_SELFSPEC_FLAG_LIMITED,
 	  0,
 	  MOO_FPDEC_NAMED_INSTVARS,
-	  MOO_CLASS_SPEC_FLAG_INDEXED,
+	  MOO_CLASS_SPEC_FLAG_IMMUTABLE,
 	  MOO_OBJ_TYPE_OOP,
 	  MOO_OFFSETOF(moo_t, _fixed_point_decimal) },
 
diff --git a/moo/lib/moo-prv.h b/moo/lib/moo-prv.h
index ecd3168..9808614 100644
--- a/moo/lib/moo-prv.h
+++ b/moo/lib/moo-prv.h
@@ -1371,10 +1371,86 @@ moo_oop_t moo_makefpdec (
 );
 
 moo_oop_t moo_truncfpdecval (
-	moo_t*      moo,
-	moo_oop_t   iv,
-	moo_ooi_t   cs,
-	moo_ooi_t   ns
+	moo_t*       moo,
+	moo_oop_t    iv, /* integer */
+	moo_ooi_t    cs, /* current scale */
+	moo_ooi_t    ns  /* new scale */
+);
+
+moo_oop_t moo_addnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_subnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_mulnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_mltnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_divnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_gtnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_genums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_ltnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_lenums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_eqnums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_nenums (
+	moo_t*       moo,
+	moo_oop_t    x,
+	moo_oop_t    y
+);
+
+moo_oop_t moo_sqrtnum (
+	moo_t*       moo,
+	moo_oop_t    x
+);
+
+moo_oop_t moo_absnum (
+	moo_t*       moo,
+	moo_oop_t    x
 );
 
 /* ========================================================================= */