diff --git a/gcc/combine.cc b/gcc/combine.cc
index 5aa0ec5c45a..bdf6f635c80 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -200,7 +200,7 @@ struct reg_stat_type {
 
   unsigned HOST_WIDE_INT	last_set_nonzero_bits;
   char				last_set_sign_bit_copies;
-  ENUM_BITFIELD(machine_mode)	last_set_mode : 8;
+  ENUM_BITFIELD(machine_mode)	last_set_mode : RTX_MACHINE_MODE_BITSIZE;
 
   /* Set nonzero if references to register n in expressions should not be
      used.  last_set_invalid is set nonzero when this register is being
@@ -235,7 +235,7 @@ struct reg_stat_type {
      truncation if we know that value already contains a truncated
      value.  */
 
-  ENUM_BITFIELD(machine_mode)	truncated_to_mode : 8;
+  ENUM_BITFIELD(machine_mode)	truncated_to_mode : RTX_MACHINE_MODE_BITSIZE;
 };
 
 
diff --git a/gcc/cse.cc b/gcc/cse.cc
index b10c9b0c94d..fe594c1bc3d 100644
--- a/gcc/cse.cc
+++ b/gcc/cse.cc
@@ -250,8 +250,8 @@ struct qty_table_elem
   unsigned int first_reg, last_reg;
   /* The sizes of these fields should match the sizes of the
      code and mode fields of struct rtx_def (see rtl.h).  */
-  ENUM_BITFIELD(rtx_code) comparison_code : 16;
-  ENUM_BITFIELD(machine_mode) mode : 8;
+  ENUM_BITFIELD(rtx_code) comparison_code : RTX_CODE_BITSIZE;
+  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
 };
 
 /* The table of all qtys, indexed by qty number.  */
@@ -406,7 +406,7 @@ struct table_elt
   int regcost;
   /* The size of this field should match the size
      of the mode field of struct rtx_def (see rtl.h).  */
-  ENUM_BITFIELD(machine_mode) mode : 8;
+  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
   char in_memory;
   char is_const;
   char flag;
@@ -4155,7 +4155,7 @@ struct set
   /* Original machine mode, in case it becomes a CONST_INT.
      The size of this field should match the size of the mode
      field of struct rtx_def (see rtl.h).  */
-  ENUM_BITFIELD(machine_mode) mode : 8;
+  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
   /* Hash value of constant equivalent for SET_SRC.  */
   unsigned src_const_hash;
   /* A constant equivalent for SET_SRC, if any.  */
diff --git a/gcc/genopinit.cc b/gcc/genopinit.cc
index 83cb7504fa1..2add8b925da 100644
--- a/gcc/genopinit.cc
+++ b/gcc/genopinit.cc
@@ -182,7 +182,8 @@ main (int argc, const char **argv)
 
   progname = "genopinit";
 
-  if (NUM_OPTABS > 0xffff || MAX_MACHINE_MODE >= 0xff)
+  if (NUM_OPTABS > 0xffff
+    || MAX_MACHINE_MODE >= ((1 << RTX_MACHINE_MODE_BITSIZE) - 1))
     fatal ("genopinit range assumptions invalid");
 
   if (!init_rtx_reader_args_cb (argc, argv, handle_arg))
diff --git a/gcc/ira-int.h b/gcc/ira-int.h
index e2de47213b4..124e14200b1 100644
--- a/gcc/ira-int.h
+++ b/gcc/ira-int.h
@@ -280,11 +280,15 @@ struct ira_allocno
   /* Regno for allocno or cap.  */
   int regno;
   /* Mode of the allocno which is the mode of the corresponding
-     pseudo-register.  */
-  ENUM_BITFIELD (machine_mode) mode : 8;
+     pseudo-register.  Note the bitsize of mode should be exactly
+     the same as the definition of rtx_def, aka RTX_MACHINE_MODE_BITSIZE
+     in rtl.h.  */
+  ENUM_BITFIELD (machine_mode) mode : 16;
   /* Widest mode of the allocno which in at least one case could be
-     for paradoxical subregs where wmode > mode.  */
-  ENUM_BITFIELD (machine_mode) wmode : 8;
+     for paradoxical subregs where wmode > mode.  Note the bitsize of
+     wmode should be exactly the same as the definition of rtx_def,
+     aka RTX_MACHINE_MODE_BITSIZE in rtl.h.  */
+  ENUM_BITFIELD (machine_mode) wmode : 16;
   /* Register class which should be used for allocation for given
      allocno.  NO_REGS means that we should use memory.  */
   ENUM_BITFIELD (reg_class) aclass : 16;
diff --git a/gcc/ree.cc b/gcc/ree.cc
index 413aec7c8eb..fb011bc907c 100644
--- a/gcc/ree.cc
+++ b/gcc/ree.cc
@@ -567,7 +567,7 @@ enum ext_modified_kind
 struct ATTRIBUTE_PACKED ext_modified
 {
   /* Mode from which ree has zero or sign extended the destination.  */
-  ENUM_BITFIELD(machine_mode) mode : 8;
+  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
 
   /* Kind of modification of the insn.  */
   ENUM_BITFIELD(ext_modified_kind) kind : 2;
diff --git a/gcc/rtl-ssa/accesses.h b/gcc/rtl-ssa/accesses.h
index c5180b9308a..2e73004cafa 100644
--- a/gcc/rtl-ssa/accesses.h
+++ b/gcc/rtl-ssa/accesses.h
@@ -253,8 +253,10 @@ private:
   // Bits for future expansion.
   unsigned int m_spare : 2;
 
-  // The value returned by the accessor above.
-  machine_mode m_mode : 8;
+  // The value returned by the accessor above.  Note the bitsize of
+  // m_mode should be exactly the same as the definition of rtx_def,
+  // aka RTX_MACHINE_MODE_BITSIZE in rtl.h.
+  machine_mode m_mode : 16;
 };
 
 // A contiguous array of access_info pointers.  Used to represent a
diff --git a/gcc/rtl.h b/gcc/rtl.h
index f634cab730b..a18ecf7632f 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -63,6 +63,9 @@ enum rtx_code  {
 # define NON_GENERATOR_NUM_RTX_CODE ((int) MATCH_OPERAND)
 #endif
 
+#define RTX_CODE_BITSIZE 8
+#define RTX_MACHINE_MODE_BITSIZE 16
+
 /* Register Transfer Language EXPRESSIONS CODE CLASSES */
 
 enum rtx_class  {
@@ -310,10 +313,10 @@ struct GTY((desc("0"), tag("0"),
 	    chain_next ("RTX_NEXT (&%h)"),
 	    chain_prev ("RTX_PREV (&%h)"))) rtx_def {
   /* The kind of expression this is.  */
-  ENUM_BITFIELD(rtx_code) code: 16;
+  ENUM_BITFIELD(rtx_code) code: RTX_CODE_BITSIZE;
 
   /* The kind of value the expression has.  */
-  ENUM_BITFIELD(machine_mode) mode : 8;
+  ENUM_BITFIELD(machine_mode) mode : RTX_MACHINE_MODE_BITSIZE;
 
   /* 1 in a MEM if we should keep the alias set for this mem unchanged
      when we access a component.
@@ -2164,7 +2167,7 @@ subreg_shape::operator != (const subreg_shape &other) const
 inline unsigned HOST_WIDE_INT
 subreg_shape::unique_id () const
 {
-  { STATIC_ASSERT (MAX_MACHINE_MODE <= 256); }
+  { STATIC_ASSERT (MAX_MACHINE_MODE <= (1 << RTX_MACHINE_MODE_BITSIZE)); }
   { STATIC_ASSERT (NUM_POLY_INT_COEFFS <= 3); }
   { STATIC_ASSERT (sizeof (offset.coeffs[0]) <= 2); }
   int res = (int) inner_mode + ((int) outer_mode << 8);
diff --git a/gcc/rtlanal.h b/gcc/rtlanal.h
index 5fbed816e20..15aba0dec7a 100644
--- a/gcc/rtlanal.h
+++ b/gcc/rtlanal.h
@@ -99,8 +99,9 @@ public:
   unsigned int flags : 16;
 
   /* The mode of the reference.  If IS_MULTIREG, this is the mode of
-     REGNO - MULTIREG_OFFSET.  */
-  machine_mode mode : 8;
+     REGNO - MULTIREG_OFFSET.  Note the bitsize of mode should be exactly
+     the same as the definition of rtx_def,  */
+  machine_mode mode : 16;
 
   /* If IS_MULTIREG, the offset of REGNO from the start of the register.  */
   unsigned int multireg_offset : 8;
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index a1aea136e75..001d232f433 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1680,8 +1680,11 @@ struct GTY(()) tree_type_common {
   tree attributes;
   unsigned int uid;
 
+  /* Note the bitsize of wmode should be exactly the same as the
+     definition of rtx_def,  aka RTX_MACHINE_MODE_BITSIZE in rtl.h.  */
+  ENUM_BITFIELD(machine_mode) mode : 16;
+
   unsigned int precision : 16;
-  ENUM_BITFIELD(machine_mode) mode : 8;
   unsigned lang_flag_0 : 1;
   unsigned lang_flag_1 : 1;
   unsigned lang_flag_2 : 1;
@@ -1712,7 +1715,7 @@ struct GTY(()) tree_type_common {
   unsigned empty_flag : 1;
   unsigned indivisible_p : 1;
   unsigned no_named_args_stdarg_p : 1;
-  unsigned spare : 9;
+  unsigned spare : 1;
 
   alias_set_type alias_set;
   tree pointer_to;
@@ -1770,7 +1773,9 @@ struct GTY(()) tree_decl_common {
   struct tree_decl_minimal common;
   tree size;
 
-  ENUM_BITFIELD(machine_mode) mode : 8;
+  /* Note the bitsize of wmode should be exactly the same as the
+     definition of rtx_def,  aka RTX_MACHINE_MODE_BITSIZE in rtl.h.  */
+  ENUM_BITFIELD(machine_mode) mode : 16;
 
   unsigned nonlocal_flag : 1;
   unsigned virtual_flag : 1;
