diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index 7c4c0a4..6e03548 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -149,7 +149,7 @@ ar_type;
    nor CONTINUE; otherwise it is identical to ST_LABEL_TARGET.  */
 typedef enum
 { ST_LABEL_UNKNOWN = 1, ST_LABEL_TARGET, ST_LABEL_DO_TARGET,
-  ST_LABEL_BAD_TARGET, ST_LABEL_FORMAT
+  ST_LABEL_BAD_TARGET, ST_LABEL_FORMAT = 0
 }
 gfc_sl_type;
 
@@ -595,7 +595,11 @@ gfc_reverse;
 /************************* Structures *****************************/
 
 /* Used for keeping things in balanced binary trees.  */
-#define BBT_HEADER(self) int priority; struct self *left, *right
+struct gfc_bbt {
+  int priority;
+  gfc_bbt *left;
+  gfc_bbt *right;
+};
 
 #define NAMED_INTCST(a,b,c,d) a,
 #define NAMED_KINDARRAY(a,b,c,d) a,
@@ -1075,10 +1079,8 @@ gfc_omp_clauses;
 /* The gfc_st_label structure is a BBT attached to a namespace that
    records the usage of statement labels within that space.  */
 
-typedef struct gfc_st_label
+struct gfc_st_label : public gfc_bbt
 {
-  BBT_HEADER(gfc_st_label);
-
   int value;
 
   gfc_sl_type defined, referenced;
@@ -1088,8 +1090,7 @@ typedef struct gfc_st_label
   tree backend_decl;
 
   locus where;
-}
-gfc_st_label;
+};
 
 
 /* gfc_interface()-- Interfaces are lists of symbols strung together.  */
@@ -1325,9 +1326,8 @@ gfc_use_list;
    several symtrees pointing to the same symbol node via USE
    statements.  */
 
-typedef struct gfc_symtree
+struct gfc_symtree : public gfc_bbt
 {
-  BBT_HEADER (gfc_symtree);
   const char *name;
   int ambiguous;
   union
@@ -1338,8 +1338,7 @@ typedef struct gfc_symtree
     gfc_typebound_proc *tb;
   }
   n;
-}
-gfc_symtree;
+};
 
 /* A linked list of derived types in the namespace.  */
 typedef struct gfc_dt_list
@@ -1464,10 +1463,8 @@ enum gfc_symbol_type
   GSYM_MODULE, GSYM_COMMON, GSYM_BLOCK_DATA
 };
 
-typedef struct gfc_gsymbol
+struct gfc_gsymbol : public gfc_bbt
 {
-  BBT_HEADER(gfc_gsymbol);
-
   const char *name;
   const char *sym_name;
   const char *mod_name;
@@ -1477,8 +1474,7 @@ typedef struct gfc_gsymbol
   int defined, used;
   locus where;
   gfc_namespace *ns;
-}
-gfc_gsymbol;
+};
 
 extern gfc_gsymbol *gfc_gsym_root;
 
@@ -2911,9 +2907,9 @@ void gfc_init_coarray_decl (bool);
 bool gfc_inline_intrinsic_function_p (gfc_expr *);
 
 /* bbt.c */
-typedef int (*compare_fn) (void *, void *);
-void gfc_insert_bbt (void *, void *, compare_fn);
-void gfc_delete_bbt (void *, void *, compare_fn);
+typedef int (*compare_fn) (const gfc_bbt *, const gfc_bbt *);
+void gfc_insert_bbt (void *, gfc_bbt *, compare_fn);
+void gfc_delete_bbt (void *, gfc_bbt *, compare_fn);
 
 /* dump-parse-tree.c */
 void gfc_dump_parse_tree (gfc_namespace *, FILE *);
diff --git a/gcc/fortran/bbt.c b/gcc/fortran/bbt.c
index 000f04b..7064fa3 100644
--- a/gcc/fortran/bbt.c
+++ b/gcc/fortran/bbt.c
@@ -41,11 +41,6 @@ along with GCC; see the file COPYING3.  If not see
 #include "coretypes.h"
 #include "gfortran.h"
 
-typedef struct gfc_treap
-{
-  BBT_HEADER (gfc_treap);
-}
-gfc_bbt;
 
 /* Simple linear congruential pseudorandom number generator.  The
    period of this generator is 44071, which is plenty for our
@@ -128,14 +123,11 @@ insert (gfc_bbt *new_bbt, gfc_bbt *t, compare_fn compare)
    already exists.  */
 
 void
-gfc_insert_bbt (void *root, void *new_node, compare_fn compare)
+gfc_insert_bbt (void *root, gfc_bbt *new_node, compare_fn compare)
 {
-  gfc_bbt **r, *n;
-
-  r = (gfc_bbt **) root;
-  n = (gfc_bbt *) new_node;
-  n->priority = pseudo_random ();
-  *r = insert (n, *r, compare);
+  gfc_bbt **r = (gfc_bbt **)root;
+  new_node->priority = pseudo_random ();
+  *r = insert (new_node, *r, compare);
 }
 
 static gfc_bbt *
@@ -190,10 +182,8 @@ delete_treap (gfc_bbt *old, gfc_bbt *t, compare_fn compare)
 
 
 void
-gfc_delete_bbt (void *root, void *old, compare_fn compare)
+gfc_delete_bbt (void *root, gfc_bbt *old, compare_fn compare)
 {
-  gfc_bbt **t;
-
-  t = (gfc_bbt **) root;
-  *t = delete_treap ((gfc_bbt *) old, *t, compare);
+  gfc_bbt **r = (gfc_bbt **)root;
+  *r = delete_treap (old, *r, compare);
 }
diff --git a/gcc/fortran/class.c b/gcc/fortran/class.c
index 21a91ba..35adedf 100644
--- a/gcc/fortran/class.c
+++ b/gcc/fortran/class.c
@@ -658,10 +658,10 @@ add_procs_to_declared_vtab1 (gfc_symtree *st, gfc_symbol *vtype)
     return;
 
   if (st->left)
-    add_procs_to_declared_vtab1 (st->left, vtype);
+    add_procs_to_declared_vtab1 ((gfc_symtree *)st->left, vtype);
 
   if (st->right)
-    add_procs_to_declared_vtab1 (st->right, vtype);
+    add_procs_to_declared_vtab1 ((gfc_symtree *)st->right, vtype);
 
   if (st->n.tb && !st->n.tb->error 
       && !st->n.tb->is_generic && st->n.tb->u.specific)
diff --git a/gcc/fortran/dump-parse-tree.c b/gcc/fortran/dump-parse-tree.c
index cb8fab4..b6da3d0 100644
--- a/gcc/fortran/dump-parse-tree.c
+++ b/gcc/fortran/dump-parse-tree.c
@@ -938,8 +938,8 @@ traverse_uop (gfc_symtree *st, void (*func) (gfc_user_op *))
 
   (*func) (st->n.uop);
 
-  traverse_uop (st->left, func);
-  traverse_uop (st->right, func);
+  traverse_uop ((gfc_symtree *)st->left, func);
+  traverse_uop ((gfc_symtree *)st->right, func);
 }
 
 
diff --git a/gcc/fortran/interface.c b/gcc/fortran/interface.c
index 482c294..b18bcd5 100644
--- a/gcc/fortran/interface.c
+++ b/gcc/fortran/interface.c
@@ -3321,9 +3321,9 @@ find_symtree0 (gfc_symtree *root, gfc_symbol *sym)
 
   st = NULL;
   if (root->left)
-    st = find_symtree0 (root->left, sym);
+    st = find_symtree0 ((gfc_symtree *)root->left, sym);
   if (root->right && ! st)
-    st = find_symtree0 (root->right, sym);
+    st = find_symtree0 ((gfc_symtree *)root->right, sym);
   return st;
 }
 
diff --git a/gcc/fortran/io.c b/gcc/fortran/io.c
index 428799c..298efb2 100644
--- a/gcc/fortran/io.c
+++ b/gcc/fortran/io.c
@@ -29,8 +29,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "parse.h"
 
 gfc_st_label
-format_asterisk = {0, NULL, NULL, -1, ST_LABEL_FORMAT, ST_LABEL_FORMAT, NULL,
-		   0, {NULL, NULL}};
+format_asterisk;
 
 typedef struct
 {
diff --git a/gcc/fortran/module.c b/gcc/fortran/module.c
index a4ff199..4de8e61 100644
--- a/gcc/fortran/module.c
+++ b/gcc/fortran/module.c
@@ -138,9 +138,8 @@ enum gfc_wsym_state
   WRITTEN
 };
 
-typedef struct pointer_info
+struct pointer_info : public gfc_bbt
 {
-  BBT_HEADER (pointer_info);
   int integer;
   pointer_t type;
 
@@ -174,8 +173,7 @@ typedef struct pointer_info
   }
   u;
 
-}
-pointer_info;
+};
 
 #define gfc_get_pointer_info() XCNEW (pointer_info)
 
@@ -225,8 +223,8 @@ free_pi_tree (pointer_info *p)
   if (p->fixup != NULL)
     gfc_internal_error ("free_pi_tree(): Unresolved fixup");
 
-  free_pi_tree (p->left);
-  free_pi_tree (p->right);
+  free_pi_tree ((pointer_info *)p->left);
+  free_pi_tree ((pointer_info *)p->right);
 
   if (iomode == IO_INPUT)
     {
@@ -243,12 +241,12 @@ free_pi_tree (pointer_info *p)
    module.  */
 
 static int
-compare_pointers (void *_sn1, void *_sn2)
+compare_pointers (const gfc_bbt *_sn1, const gfc_bbt *_sn2)
 {
-  pointer_info *sn1, *sn2;
+  const pointer_info *sn1, *sn2;
 
-  sn1 = (pointer_info *) _sn1;
-  sn2 = (pointer_info *) _sn2;
+  sn1 = (const pointer_info *) _sn1;
+  sn2 = (const pointer_info *) _sn2;
 
   if (sn1->u.pointer < sn2->u.pointer)
     return -1;
@@ -263,12 +261,12 @@ compare_pointers (void *_sn1, void *_sn2)
    module.  */
 
 static int
-compare_integers (void *_sn1, void *_sn2)
+compare_integers (const gfc_bbt *_sn1, const gfc_bbt *_sn2)
 {
-  pointer_info *sn1, *sn2;
+  const pointer_info *sn1, *sn2;
 
-  sn1 = (pointer_info *) _sn1;
-  sn2 = (pointer_info *) _sn2;
+  sn1 = (const pointer_info *) _sn1;
+  sn2 = (const pointer_info *) _sn2;
 
   if (sn1->integer < sn2->integer)
     return -1;
@@ -323,7 +321,7 @@ find_pointer (void *gp)
     {
       if (p->u.pointer == gp)
 	break;
-      p = (gp < p->u.pointer) ? p->left : p->right;
+      p =  (pointer_info *)((gp < p->u.pointer) ?p->left : p->right);
     }
 
   return p;
@@ -372,7 +370,7 @@ get_integer (int integer)
       if (c == 0)
 	break;
 
-      p = (c < 0) ? p->left : p->right;
+      p = (pointer_info *)((c < 0) ? p->left : p->right);
     }
 
   if (p != NULL)
@@ -401,11 +399,11 @@ fp2 (pointer_info *p, const void *target)
   if (p->u.pointer == target)
     return p;
 
-  q = fp2 (p->left, target);
+  q = fp2 ((pointer_info *)p->left, target);
   if (q != NULL)
     return q;
 
-  return fp2 (p->right, target);
+  return fp2 ((pointer_info *)p->right, target);
 }
 
 
@@ -843,13 +841,11 @@ find_use_operator (gfc_intrinsic_op op)
    as symbols are read.  The tree is searched as we load new symbols
    to see if it already exists someplace in the namespace.  */
 
-typedef struct true_name
+struct true_name : public gfc_bbt
 {
-  BBT_HEADER (true_name);
   const char *name;
   gfc_symbol *sym;
-}
-true_name;
+};
 
 static true_name *true_name_root;
 
@@ -857,13 +853,13 @@ static true_name *true_name_root;
 /* Compare two true_name structures.  */
 
 static int
-compare_true_names (void *_t1, void *_t2)
+compare_true_names (const gfc_bbt *_t1, const gfc_bbt *_t2)
 {
-  true_name *t1, *t2;
+  const true_name *t1, *t2;
   int c;
 
-  t1 = (true_name *) _t1;
-  t2 = (true_name *) _t2;
+  t1 = (const true_name *) _t1;
+  t2 = (const true_name *) _t2;
 
   c = ((t1->sym->module > t2->sym->module)
        - (t1->sym->module < t2->sym->module));
@@ -894,11 +890,11 @@ find_true_name (const char *name, const char *module)
   p = true_name_root;
   while (p != NULL)
     {
-      c = compare_true_names ((void *) (&t), (void *) p);
+      c = compare_true_names (&t, p);
       if (c == 0)
 	return p->sym;
 
-      p = (c < 0) ? p->left : p->right;
+      p = (c < 0) ? (true_name *)p->left : (true_name *)p->right;
     }
 
   return NULL;
@@ -933,8 +929,8 @@ build_tnt (gfc_symtree *st)
   if (st == NULL)
     return;
 
-  build_tnt (st->left);
-  build_tnt (st->right);
+  build_tnt ((gfc_symtree *)st->left);
+  build_tnt ((gfc_symtree *)st->right);
 
   if (st->n.sym->attr.flavor == FL_DERIVED)
     name = dt_upper_string (st->n.sym->name);
@@ -965,8 +961,8 @@ free_true_name (true_name *t)
 {
   if (t == NULL)
     return;
-  free_true_name (t->left);
-  free_true_name (t->right);
+  free_true_name ((true_name *)t->left);
+  free_true_name ((true_name *)t->right);
 
   free (t);
 }
@@ -3878,10 +3874,10 @@ find_symtree_for_symbol (gfc_symtree *st, gfc_symbol *sym)
   if (st == NULL)
     return s;
 
-  s = find_symtree_for_symbol (st->right, sym);
+  s = find_symtree_for_symbol ((gfc_symtree *)st->right, sym);
   if (s != NULL)
     return s;
-  s = find_symtree_for_symbol (st->left, sym);
+  s = find_symtree_for_symbol ((gfc_symtree *)st->left, sym);
   if (s != NULL)
     return s;
 
@@ -3923,10 +3919,10 @@ find_symbol (gfc_symtree *st, const char *name,
 	return st;
     }
 
-  retval = find_symbol (st->left, name, module, generic);
+  retval = find_symbol ((gfc_symtree *)st->left, name, module, generic);
 
   if (retval == NULL)
-    retval = find_symbol (st->right, name, module, generic);
+    retval = find_symbol ((gfc_symtree *)st->right, name, module, generic);
 
   return retval;
 }
@@ -4353,8 +4349,8 @@ load_needed (pointer_info *p)
   if (p == NULL)
     return rv;
 
-  rv |= load_needed (p->left);
-  rv |= load_needed (p->right);
+  rv |= load_needed ((pointer_info *)p->left);
+  rv |= load_needed ((pointer_info *)p->right);
 
   if (p->type != P_SYMBOL || p->u.rsym.state != NEEDED)
     return rv;
@@ -4436,8 +4432,8 @@ read_cleanup (pointer_info *p)
   if (p == NULL)
     return;
 
-  read_cleanup (p->left);
-  read_cleanup (p->right);
+  read_cleanup ((pointer_info *)p->left);
+  read_cleanup ((pointer_info *)p->right);
 
   if (p->type == P_SYMBOL && p->u.rsym.state == USED && !p->u.rsym.referenced)
     {
@@ -4846,9 +4842,8 @@ gfc_check_symbol_access (gfc_symbol *sym)
 
 /* A structure to remember which commons we've already written.  */
 
-struct written_common
+struct written_common : public gfc_bbt
 {
-  BBT_HEADER(written_common);
   const char *name, *label;
 };
 
@@ -4857,29 +4852,27 @@ static struct written_common *written_commons = NULL;
 /* Comparison function used for balancing the binary tree.  */
 
 static int
-compare_written_commons (void *a1, void *b1)
+compare_written_commons (const gfc_bbt *a1, const gfc_bbt *b1)
 {
-  const char *aname = ((struct written_common *) a1)->name;
-  const char *alabel = ((struct written_common *) a1)->label;
-  const char *bname = ((struct written_common *) b1)->name;
-  const char *blabel = ((struct written_common *) b1)->label;
-  int c = strcmp (aname, bname);
+  const written_common *a = (const written_common *)a1;
+  const written_common *b = (const written_common *)b1;
+  int c = strcmp (a->name, b->name);
 
-  return (c != 0 ? c : strcmp (alabel, blabel));
+  return (c != 0 ? c : strcmp (a->label, b->label));
 }
 
 /* Free a list of written commons.  */
 
 static void
-free_written_common (struct written_common *w)
+free_written_common (written_common *w)
 {
   if (!w)
     return;
 
   if (w->left)
-    free_written_common (w->left);
+    free_written_common ((written_common *)w->left);
   if (w->right)
-    free_written_common (w->right);
+    free_written_common ((written_common *)w->right);
 
   free (w);
 }
@@ -4899,7 +4892,7 @@ write_common_0 (gfc_symtree *st, bool this_module)
   if (st == NULL)
     return;
 
-  write_common_0 (st->left, this_module);
+  write_common_0 ((gfc_symtree *)st->left, this_module);
 
   /* We will write out the binding label, or "" if no label given.  */
   name = st->n.common->name;
@@ -4915,7 +4908,7 @@ write_common_0 (gfc_symtree *st, bool this_module)
       if (c == 0)
 	write_me = false;
 
-      w = (c < 0) ? w->left : w->right;
+      w =  (written_common *)((c < 0) ? w->left : w->right);
     }
 
   if (this_module && p->use_assoc)
@@ -4946,7 +4939,7 @@ write_common_0 (gfc_symtree *st, bool this_module)
       gfc_insert_bbt (&written_commons, w, compare_written_commons);
     }
 
-  write_common_0 (st->right, this_module);
+  write_common_0 ((gfc_symtree *)st->right, this_module);
 }
 
 
@@ -5117,7 +5110,7 @@ write_symbol0 (gfc_symtree *st)
   if (st == NULL)
     return;
 
-  write_symbol0 (st->left);
+  write_symbol0 ((gfc_symtree *)st->left);
 
   sym = st->n.sym;
   if (sym->module == NULL)
@@ -5143,7 +5136,7 @@ write_symbol0 (gfc_symtree *st)
 	}
     }
 
-  write_symbol0 (st->right);
+  write_symbol0 ((gfc_symtree *)st->right);
 }
 
 
@@ -5162,7 +5155,7 @@ write_symbol1 (pointer_info *p)
   if (!p)
     return 0;
 
-  result = write_symbol1 (p->left);
+  result = write_symbol1 ((pointer_info *)p->left);
 
   if (!(p->type != P_SYMBOL || p->u.wsym.state != NEEDS_WRITE))
     {
@@ -5171,7 +5164,7 @@ write_symbol1 (pointer_info *p)
       result = 1;
     }
 
-  result |= write_symbol1 (p->right);
+  result |= write_symbol1 ((pointer_info *)p->right);
   return result;
 }
 
@@ -5201,8 +5194,8 @@ write_generic (gfc_symtree *st)
   if (st == NULL)
     return;
 
-  write_generic (st->left);
-  write_generic (st->right);
+  write_generic ((gfc_symtree *)st->left);
+  write_generic ((gfc_symtree *)st->right);
 
   sym = st->n.sym;
   if (!sym || check_unique_name (st->name))
diff --git a/gcc/fortran/parse.c b/gcc/fortran/parse.c
index 44b1900..f1a5aed 100644
--- a/gcc/fortran/parse.c
+++ b/gcc/fortran/parse.c
@@ -4405,8 +4405,8 @@ clean_up_modules (gfc_gsymbol *gsym)
   if (gsym == NULL)
     return;
 
-  clean_up_modules (gsym->left);
-  clean_up_modules (gsym->right);
+  clean_up_modules ((gfc_gsymbol *)gsym->left);
+  clean_up_modules ((gfc_gsymbol *)gsym->right);
 
   if (gsym->type != GSYM_MODULE || !gsym->ns)
     return;
diff --git a/gcc/fortran/resolve.c b/gcc/fortran/resolve.c
index ac5a362..3968d7e 100644
--- a/gcc/fortran/resolve.c
+++ b/gcc/fortran/resolve.c
@@ -953,9 +953,9 @@ resolve_common_blocks (gfc_symtree *common_root)
     return;
 
   if (common_root->left)
-    resolve_common_blocks (common_root->left);
+    resolve_common_blocks ((gfc_symtree *)common_root->left);
   if (common_root->right)
-    resolve_common_blocks (common_root->right);
+    resolve_common_blocks ((gfc_symtree *)common_root->right);
 
   resolve_common_vars (common_root->n.common->head, true);
 
@@ -11803,9 +11803,9 @@ ensure_not_abstract_walker (gfc_symbol* sub, gfc_symtree* st)
   if (!st)
     return SUCCESS;
 
-  if (ensure_not_abstract_walker (sub, st->left) == FAILURE)
+  if (ensure_not_abstract_walker (sub, (gfc_symtree *)st->left) == FAILURE)
     return FAILURE;
-  if (ensure_not_abstract_walker (sub, st->right) == FAILURE)
+  if (ensure_not_abstract_walker (sub, (gfc_symtree *)st->right) == FAILURE)
     return FAILURE;
 
   if (st->n.tb && st->n.tb->deferred)
@@ -13627,7 +13627,7 @@ warn_unused_fortran_label (gfc_st_label *label)
   if (label == NULL)
     return;
 
-  warn_unused_fortran_label (label->left);
+  warn_unused_fortran_label ((gfc_st_label *)label->left);
 
   if (label->defined == ST_LABEL_UNKNOWN)
     return;
@@ -13648,7 +13648,7 @@ warn_unused_fortran_label (gfc_st_label *label)
       break;
     }
 
-  warn_unused_fortran_label (label->right);
+  warn_unused_fortran_label ((gfc_st_label *)label->right);
 }
 
 
@@ -14143,8 +14143,8 @@ gfc_resolve_uops (gfc_symtree *symtree)
   if (symtree == NULL)
     return;
 
-  gfc_resolve_uops (symtree->left);
-  gfc_resolve_uops (symtree->right);
+  gfc_resolve_uops ((gfc_symtree *)symtree->left);
+  gfc_resolve_uops ((gfc_symtree *)symtree->right);
 
   for (itr = symtree->n.uop->op; itr; itr = itr->next)
     check_uop_procedure (itr->sym, itr->sym->declared_at);
diff --git a/gcc/fortran/symbol.c b/gcc/fortran/symbol.c
index 5a1e5ad..1c5b1aa 100644
--- a/gcc/fortran/symbol.c
+++ b/gcc/fortran/symbol.c
@@ -1921,8 +1921,8 @@ switch_types (gfc_symtree *st, gfc_symbol *from, gfc_symbol *to)
   if (sym->ts.type == BT_DERIVED && sym->ts.u.derived == from)
     sym->ts.u.derived = to;
 
-  switch_types (st->left, from, to);
-  switch_types (st->right, from, to);
+  switch_types ((gfc_symtree *)st->left, from, to);
+  switch_types ((gfc_symtree *)st->right, from, to);
 }
 
 
@@ -2090,10 +2090,10 @@ free_components (gfc_component *p)
    binary tree.  */
 
 static int
-compare_st_labels (void *a1, void *b1)
+compare_st_labels (const gfc_bbt *a1, const gfc_bbt *b1)
 {
-  int a = ((gfc_st_label *) a1)->value;
-  int b = ((gfc_st_label *) b1)->value;
+  int a = ((const gfc_st_label *) a1)->value;
+  int b = ((const gfc_st_label *) b1)->value;
 
   return (b - a);
 }
@@ -2128,8 +2128,8 @@ free_st_labels (gfc_st_label *label)
   if (label == NULL)
     return;
 
-  free_st_labels (label->left);
-  free_st_labels (label->right);
+  free_st_labels ((gfc_st_label *)label->left);
+  free_st_labels ((gfc_st_label *)label->right);
   
   if (label->format != NULL)
     gfc_free_expr (label->format);
@@ -2165,9 +2165,9 @@ gfc_get_st_label (int labelno)
 	return lp;
 
       if (lp->value < labelno)
-	lp = lp->left;
+	lp = (gfc_st_label *)lp->left;
       else
-	lp = lp->right;
+	lp = (gfc_st_label *)lp->right;
     }
 
   lp = XCNEW (gfc_st_label);
@@ -2376,12 +2376,10 @@ gfc_get_namespace (gfc_namespace *parent, int parent_types)
 /* Comparison function for symtree nodes.  */
 
 static int
-compare_symtree (void *_st1, void *_st2)
+compare_symtree (const gfc_bbt *_st1, const gfc_bbt *_st2)
 {
-  gfc_symtree *st1, *st2;
-
-  st1 = (gfc_symtree *) _st1;
-  st2 = (gfc_symtree *) _st2;
+  const gfc_symtree *st1 = (const gfc_symtree *) _st1;
+  const gfc_symtree *st2 = (const gfc_symtree *) _st2;
 
   return strcmp (st1->name, st2->name);
 }
@@ -2432,7 +2430,7 @@ gfc_find_symtree (gfc_symtree *st, const char *name)
       if (c == 0)
 	return st;
 
-      st = (c < 0) ? st->left : st->right;
+      st = (gfc_symtree *)((c < 0) ? st->left : st->right);
     }
 
   return NULL;
@@ -3072,8 +3070,8 @@ free_tb_tree (gfc_symtree *t)
   if (t == NULL)
     return;
 
-  free_tb_tree (t->left);
-  free_tb_tree (t->right);
+  free_tb_tree ((gfc_symtree *)t->left);
+  free_tb_tree ((gfc_symtree *)t->right);
 
   /* TODO: Free type-bound procedure structs themselves; probably needs some
      sort of ref-counting mechanism.  */
@@ -3091,8 +3089,8 @@ free_common_tree (gfc_symtree * common_tree)
   if (common_tree == NULL)
     return;
 
-  free_common_tree (common_tree->left);
-  free_common_tree (common_tree->right);
+  free_common_tree ((gfc_symtree *)common_tree->left);
+  free_common_tree ((gfc_symtree *)common_tree->right);
 
   free (common_tree);
 }  
@@ -3107,8 +3105,8 @@ free_uop_tree (gfc_symtree *uop_tree)
   if (uop_tree == NULL)
     return;
 
-  free_uop_tree (uop_tree->left);
-  free_uop_tree (uop_tree->right);
+  free_uop_tree ((gfc_symtree *)uop_tree->left);
+  free_uop_tree ((gfc_symtree *)uop_tree->right);
 
   gfc_free_interface (uop_tree->n.uop->op);
   free (uop_tree->n.uop);
@@ -3125,8 +3123,8 @@ free_sym_tree (gfc_symtree *sym_tree)
   if (sym_tree == NULL)
     return;
 
-  free_sym_tree (sym_tree->left);
-  free_sym_tree (sym_tree->right);
+  free_sym_tree ((gfc_symtree *)sym_tree->left);
+  free_sym_tree ((gfc_symtree *)sym_tree->right);
 
   gfc_release_symbol (sym_tree->n.sym);
   free (sym_tree);
@@ -3349,9 +3347,9 @@ count_st_nodes (const gfc_symtree *st)
   if (!st)
     return 0;
 
-  nodes = count_st_nodes (st->left);
+  nodes = count_st_nodes ((const gfc_symtree *)st->left);
   nodes++;
-  nodes += count_st_nodes (st->right);
+  nodes += count_st_nodes ((const gfc_symtree *)st->right);
 
   return nodes;
 }
@@ -3365,9 +3363,9 @@ fill_st_vector (gfc_symtree *st, gfc_symtree **st_vec, unsigned node_cntr)
   if (!st)
     return node_cntr;
 
-  node_cntr = fill_st_vector (st->left, st_vec, node_cntr);
+  node_cntr = fill_st_vector ((gfc_symtree *)st->left, st_vec, node_cntr);
   st_vec[node_cntr++] = st;
-  node_cntr = fill_st_vector (st->right, st_vec, node_cntr);
+  node_cntr = fill_st_vector ((gfc_symtree *)st->right, st_vec, node_cntr);
 
   return node_cntr;
 }
@@ -3524,7 +3522,7 @@ gfc_find_gsymbol (gfc_gsymbol *symbol, const char *name)
       if (!c)
 	return symbol;
 
-      symbol = (c < 0) ? symbol->left : symbol->right;
+      symbol = (gfc_gsymbol *)((c < 0) ? symbol->left : symbol->right);
     }
 
   return NULL;
@@ -3534,12 +3532,12 @@ gfc_find_gsymbol (gfc_gsymbol *symbol, const char *name)
 /* Compare two global symbols. Used for managing the BB tree.  */
 
 static int
-gsym_compare (void *_s1, void *_s2)
+gsym_compare (const gfc_bbt *_s1, const gfc_bbt *_s2)
 {
-  gfc_gsymbol *s1, *s2;
+  const gfc_gsymbol *s1, *s2;
 
-  s1 = (gfc_gsymbol *) _s1;
-  s2 = (gfc_gsymbol *) _s2;
+  s1 = (const gfc_gsymbol *) _s1;
+  s2 = (const gfc_gsymbol *) _s2;
   return strcmp (s1->name, s2->name);
 }