diff --git a/upb/def.c b/upb/def.c
index f816c4fe11..38ef9fadba 100644
--- a/upb/def.c
+++ b/upb/def.c
@@ -106,6 +106,12 @@ struct upb_filedef {
   int ext_count;
 };
 
+struct upb_symtab {
+  upb_arena *arena;
+  upb_strtable syms;  /* full_name -> packed def ptr */
+  upb_strtable files;  /* file_name -> upb_filedef* */
+};
+
 /* Inside a symtab we store tagged pointers to specific def types. */
 typedef enum {
   UPB_DEFTYPE_MSG = 0,
@@ -124,12 +130,6 @@ static upb_value pack_def(const void *ptr, upb_deftype_t type) {
   return upb_value_constptr((const void*)num);
 }
 
-struct upb_symtab {
-  upb_arena *arena;
-  upb_strtable syms;  /* full_name -> packed def ptr */
-  upb_strtable files;  /* file_name -> upb_filedef* */
-};
-
 /* isalpha() etc. from <ctype.h> are locale-dependent, which we don't want. */
 static bool upb_isbetween(char c, char low, char high) {
   return c >= low && c <= high;
@@ -825,97 +825,6 @@ void upb_oneof_iter_setdone(upb_oneof_iter *iter) {
   upb_inttable_iter_setdone(iter);
 }
 
-/* upb_filedef ****************************************************************/
-
-const char *upb_filedef_name(const upb_filedef *f) {
-  return f->name;
-}
-
-const char *upb_filedef_package(const upb_filedef *f) {
-  return f->package;
-}
-
-const char *upb_filedef_phpprefix(const upb_filedef *f) {
-  return f->phpprefix;
-}
-
-const char *upb_filedef_phpnamespace(const upb_filedef *f) {
-  return f->phpnamespace;
-}
-
-upb_syntax_t upb_filedef_syntax(const upb_filedef *f) {
-  return f->syntax;
-}
-
-int upb_filedef_msgcount(const upb_filedef *f) {
-  return f->msg_count;
-}
-
-int upb_filedef_depcount(const upb_filedef *f) {
-  return f->dep_count;
-}
-
-int upb_filedef_enumcount(const upb_filedef *f) {
-  return f->enum_count;
-}
-
-const upb_filedef *upb_filedef_dep(const upb_filedef *f, int i) {
-  return i < 0 || i >= f->dep_count ? NULL : f->deps[i];
-}
-
-const upb_msgdef *upb_filedef_msg(const upb_filedef *f, int i) {
-  return i < 0 || i >= f->msg_count ? NULL : &f->msgs[i];
-}
-
-const upb_enumdef *upb_filedef_enum(const upb_filedef *f, int i) {
-  return i < 0 || i >= f->enum_count ? NULL : &f->enums[i];
-}
-
-void upb_symtab_free(upb_symtab *s) {
-  upb_arena_free(s->arena);
-  upb_gfree(s);
-}
-
-upb_symtab *upb_symtab_new() {
-  upb_symtab *s = upb_gmalloc(sizeof(*s));
-  upb_alloc *alloc;
-
-  if (!s) {
-    return NULL;
-  }
-
-  s->arena = upb_arena_new();
-  alloc = upb_arena_alloc(s->arena);
-
-  if (!upb_strtable_init2(&s->syms, UPB_CTYPE_CONSTPTR, alloc) ||
-      !upb_strtable_init2(&s->files, UPB_CTYPE_CONSTPTR, alloc)) {
-    upb_arena_free(s->arena);
-    upb_gfree(s);
-    s = NULL;
-  }
-  return s;
-}
-
-const upb_msgdef *upb_symtab_lookupmsg(const upb_symtab *s, const char *sym) {
-  upb_value v;
-  return upb_strtable_lookup(&s->syms, sym, &v) ?
-      unpack_def(v, UPB_DEFTYPE_MSG) : NULL;
-}
-
-const upb_msgdef *upb_symtab_lookupmsg2(const upb_symtab *s, const char *sym,
-                                        size_t len) {
-  upb_value v;
-  return upb_strtable_lookup2(&s->syms, sym, len, &v) ?
-      unpack_def(v, UPB_DEFTYPE_MSG) : NULL;
-}
-
-const upb_enumdef *upb_symtab_lookupenum(const upb_symtab *s, const char *sym) {
-  upb_value v;
-  return upb_strtable_lookup(&s->syms, sym, &v) ?
-      unpack_def(v, UPB_DEFTYPE_ENUM) : NULL;
-}
-
-
 /* Code to build defs from descriptor protos. *********************************/
 
 /* There is a question of how much validation to do here.  It will be difficult
@@ -1593,8 +1502,9 @@ static bool build_filedef(
     if (!upb_strtable_lookup2(&ctx->symtab->files, dep_name.data,
                               dep_name.size, &v)) {
       upb_status_seterrf(ctx->status,
-                         "Depends on file '%s', but it has not been loaded",
-                         dep_name.data);
+                         "Depends on file '" UPB_STRVIEW_FORMAT
+                         "', but it has not been loaded",
+                         UPB_STRVIEW_ARGS(dep_name));
       return false;
     }
     file->deps[i] = upb_value_getconstptr(v);
@@ -1656,6 +1566,102 @@ static bool upb_symtab_addtotabs(upb_symtab *s, symtab_addctx *ctx,
   return true;
 }
 
+/* upb_filedef ****************************************************************/
+
+const char *upb_filedef_name(const upb_filedef *f) {
+  return f->name;
+}
+
+const char *upb_filedef_package(const upb_filedef *f) {
+  return f->package;
+}
+
+const char *upb_filedef_phpprefix(const upb_filedef *f) {
+  return f->phpprefix;
+}
+
+const char *upb_filedef_phpnamespace(const upb_filedef *f) {
+  return f->phpnamespace;
+}
+
+upb_syntax_t upb_filedef_syntax(const upb_filedef *f) {
+  return f->syntax;
+}
+
+int upb_filedef_msgcount(const upb_filedef *f) {
+  return f->msg_count;
+}
+
+int upb_filedef_depcount(const upb_filedef *f) {
+  return f->dep_count;
+}
+
+int upb_filedef_enumcount(const upb_filedef *f) {
+  return f->enum_count;
+}
+
+const upb_filedef *upb_filedef_dep(const upb_filedef *f, int i) {
+  return i < 0 || i >= f->dep_count ? NULL : f->deps[i];
+}
+
+const upb_msgdef *upb_filedef_msg(const upb_filedef *f, int i) {
+  return i < 0 || i >= f->msg_count ? NULL : &f->msgs[i];
+}
+
+const upb_enumdef *upb_filedef_enum(const upb_filedef *f, int i) {
+  return i < 0 || i >= f->enum_count ? NULL : &f->enums[i];
+}
+
+void upb_symtab_free(upb_symtab *s) {
+  upb_arena_free(s->arena);
+  upb_gfree(s);
+}
+
+upb_symtab *upb_symtab_new() {
+  upb_symtab *s = upb_gmalloc(sizeof(*s));
+  upb_alloc *alloc;
+
+  if (!s) {
+    return NULL;
+  }
+
+  s->arena = upb_arena_new();
+  alloc = upb_arena_alloc(s->arena);
+
+  if (!upb_strtable_init2(&s->syms, UPB_CTYPE_CONSTPTR, alloc) ||
+      !upb_strtable_init2(&s->files, UPB_CTYPE_CONSTPTR, alloc)) {
+    upb_arena_free(s->arena);
+    upb_gfree(s);
+    s = NULL;
+  }
+  return s;
+}
+
+const upb_msgdef *upb_symtab_lookupmsg(const upb_symtab *s, const char *sym) {
+  upb_value v;
+  return upb_strtable_lookup(&s->syms, sym, &v) ?
+      unpack_def(v, UPB_DEFTYPE_MSG) : NULL;
+}
+
+const upb_msgdef *upb_symtab_lookupmsg2(const upb_symtab *s, const char *sym,
+                                        size_t len) {
+  upb_value v;
+  return upb_strtable_lookup2(&s->syms, sym, len, &v) ?
+      unpack_def(v, UPB_DEFTYPE_MSG) : NULL;
+}
+
+const upb_enumdef *upb_symtab_lookupenum(const upb_symtab *s, const char *sym) {
+  upb_value v;
+  return upb_strtable_lookup(&s->syms, sym, &v) ?
+      unpack_def(v, UPB_DEFTYPE_ENUM) : NULL;
+}
+
+const upb_filedef *upb_symtab_lookupfile(const upb_symtab *s, const char *name) {
+  upb_value v;
+  return upb_strtable_lookup(&s->files, name, &v) ? upb_value_getconstptr(v)
+                                                  : NULL;
+}
+
 const upb_filedef *upb_symtab_addfile(
     upb_symtab *s, const google_protobuf_FileDescriptorProto *file_proto,
     upb_status *status) {
diff --git a/upb/def.h b/upb/def.h
index 2c336c52b2..9a722f3b6e 100644
--- a/upb/def.h
+++ b/upb/def.h
@@ -818,6 +818,7 @@ const upb_msgdef *upb_symtab_lookupmsg(const upb_symtab *s, const char *sym);
 const upb_msgdef *upb_symtab_lookupmsg2(
     const upb_symtab *s, const char *sym, size_t len);
 const upb_enumdef *upb_symtab_lookupenum(const upb_symtab *s, const char *sym);
+const upb_filedef *upb_symtab_lookupfile(const upb_symtab *s, const char *name);
 int upb_symtab_filecount(const upb_symtab *s);
 const upb_filedef *upb_symtab_addfile(
     upb_symtab *s, const google_protobuf_FileDescriptorProto *file,
@@ -850,10 +851,14 @@ class upb::SymbolTable {
     return MessageDefPtr(upb_symtab_lookupmsg(ptr_.get(), sym));
   }
 
-  const EnumDefPtr LookupEnum(const char *sym) const {
+  EnumDefPtr LookupEnum(const char *sym) const {
     return EnumDefPtr(upb_symtab_lookupenum(ptr_.get(), sym));
   }
 
+  FileDefPtr LookupFile(const char *name) const {
+    return FileDefPtr(upb_symtab_lookupfile(ptr_.get(), name));
+  }
+
   /* TODO: iteration? */
 
   /* Adds the given serialized FileDescriptorProto to the pool. */
diff --git a/upb/pb/compile_decoder.c b/upb/pb/compile_decoder.c
index 75cff48990..89f000a76a 100644
--- a/upb/pb/compile_decoder.c
+++ b/upb/pb/compile_decoder.c
@@ -890,6 +890,7 @@ void upb_pbcodecache_free(upb_pbcodecache *c) {
   }
 
   upb_inttable_uninit(&c->groups);
+  upb_arena_free(c->arena);
   upb_gfree(c);
 }
 
diff --git a/upb/upb.c b/upb/upb.c
index d8d27236b8..9f80639858 100644
--- a/upb/upb.c
+++ b/upb/upb.c
@@ -191,10 +191,8 @@ upb_arena *upb_arena_init(void *mem, size_t n, upb_alloc *alloc) {
     }
   }
 
-  a = mem;
-  mem = (char*)mem + sizeof(*a);
+  a = (void*)((char*)mem + n - sizeof(*a));
   n -= sizeof(*a);
-  upb_arena_addblock(a, mem, n, owned);
 
   a->alloc.func = &upb_arena_doalloc;
   a->block_alloc = &upb_alloc_global;
@@ -205,6 +203,8 @@ upb_arena *upb_arena_init(void *mem, size_t n, upb_alloc *alloc) {
   a->block_head = NULL;
   a->block_alloc = alloc;
 
+  upb_arena_addblock(a, mem, n, owned);
+
   return a;
 }