diff --git a/io_buffer.c b/io_buffer.c
index d1b2f047110a0e..0da1bf5cd8017e 100644
--- a/io_buffer.c
+++ b/io_buffer.c
@@ -648,14 +648,15 @@ rb_io_buffer_for_reading(VALUE string_or_buffer, VALUE (*callback)(VALUE, VALUE)
     }
 }
 
-/* Forward declaration: rb_io_buffer_readonly_p is defined later in this file. */
-int rb_io_buffer_readonly_p(VALUE self);
+/* Forward declaration: io_buffer_readonly_p is defined later in this file. */
+static int io_buffer_readonly_p(struct rb_io_buffer *buffer);
 
 VALUE
 rb_io_buffer_for_writing(VALUE string_or_buffer, VALUE (*callback)(VALUE, VALUE), VALUE argument)
 {
     if (rb_obj_is_kind_of(string_or_buffer, rb_cIOBuffer)) {
-        if (rb_io_buffer_readonly_p(string_or_buffer)) {
+        struct rb_io_buffer *buffer = get_io_buffer(string_or_buffer);
+        if (io_buffer_readonly_p(buffer)) {
             rb_raise(rb_eArgError, "buffer is read-only");
         }
         return callback(string_or_buffer, argument);
@@ -1509,11 +1510,9 @@ rb_io_buffer_private_p(VALUE self)
     return RBOOL(buffer->flags & RB_IO_BUFFER_PRIVATE);
 }
 
-int
-rb_io_buffer_readonly_p(VALUE self)
+static int
+io_buffer_readonly_p(struct rb_io_buffer *buffer)
 {
-    struct rb_io_buffer *buffer = get_io_buffer(self);
-
     return buffer->flags & RB_IO_BUFFER_READONLY;
 }
 
@@ -1527,9 +1526,11 @@ rb_io_buffer_readonly_p(VALUE self)
  *  backed by a frozen string or a read-only file.
  */
 static VALUE
-io_buffer_readonly_p(VALUE self)
+rb_io_buffer_readonly_p(VALUE self)
 {
-    return RBOOL(rb_io_buffer_readonly_p(self));
+    struct rb_io_buffer *buffer = get_io_buffer(self);
+
+    return RBOOL(io_buffer_readonly_p(buffer));
 }
 
 static void
@@ -4214,7 +4215,7 @@ Init_IO_Buffer(void)
     rb_define_method(rb_cIOBuffer, "shared?", rb_io_buffer_shared_p, 0);
     rb_define_method(rb_cIOBuffer, "locked?", rb_io_buffer_locked_p, 0);
     rb_define_method(rb_cIOBuffer, "private?", rb_io_buffer_private_p, 0);
-    rb_define_method(rb_cIOBuffer, "readonly?", io_buffer_readonly_p, 0);
+    rb_define_method(rb_cIOBuffer, "readonly?", rb_io_buffer_readonly_p, 0);
 
     // Locking to prevent changes while using pointer:
     // rb_define_method(rb_cIOBuffer, "lock", rb_io_buffer_lock, 0);
diff --git a/weakmap.c b/weakmap.c
index d9282de8f65a64..e67eb0146d4ef1 100644
--- a/weakmap.c
+++ b/weakmap.c
@@ -50,8 +50,6 @@ wmap_memsize(const void *ptr)
     size_t size = 0;
     if (w->table) {
         size += st_memsize(w->table);
-        /* The key and value of the table each take sizeof(VALUE) in size. */
-        size += st_table_size(w->table) * (2 * sizeof(VALUE));
     }
 
     return size;
@@ -561,8 +559,6 @@ wkmap_memsize(const void *ptr)
     size_t size = 0;
     if (w->table) {
         size += st_memsize(w->table);
-        /* Each key of the table takes sizeof(VALUE) in size. */
-        size += st_table_size(w->table) * sizeof(VALUE);
     }
 
     return size;