diff --git a/ext/openssl/ossl_ssl.c b/ext/openssl/ossl_ssl.c
index 2525d0c87..37d5837fd 100644
--- a/ext/openssl/ossl_ssl.c
+++ b/ext/openssl/ossl_ssl.c
@@ -2054,8 +2054,13 @@ ossl_ssl_read_nonblock(int argc, VALUE *argv, VALUE self)
 }
 
 static VALUE
-ossl_ssl_write_internal(VALUE self, VALUE str, VALUE opts)
+ossl_ssl_write_internal_safe(VALUE _args)
 {
+    VALUE *args = (VALUE*)_args;
+    VALUE self = args[0];
+    VALUE str = args[1];
+    VALUE opts = args[2];
+
     SSL *ssl;
     rb_io_t *fptr;
     int num, nonblock = opts != Qfalse;
@@ -2116,6 +2121,21 @@ ossl_ssl_write_internal(VALUE self, VALUE str, VALUE opts)
     }
 }
 
+static VALUE
+ossl_ssl_write_internal(VALUE self, VALUE str, VALUE opts)
+{
+    VALUE args[3] = {self, str, opts};
+    int state;
+    str = rb_str_locktmp(StringValue(str));
+    VALUE result = rb_protect(ossl_ssl_write_internal_safe, (VALUE)args, &state);
+    rb_str_unlocktmp(str);
+
+    if (state) {
+        rb_jump_tag(state);
+    }
+    return result;
+}
+
 /*
  * call-seq:
  *    ssl.syswrite(string) => Integer
diff --git a/lib/openssl/buffering.rb b/lib/openssl/buffering.rb
index 85f593af0..7ecf04c90 100644
--- a/lib/openssl/buffering.rb
+++ b/lib/openssl/buffering.rb
@@ -23,26 +23,18 @@ module OpenSSL::Buffering
   include Enumerable
 
   # A buffer which will retain binary encoding.
-  class Buffer < String
-    BINARY = Encoding::BINARY
-
-    def initialize
-      super
-
-      force_encoding(BINARY)
-    end
-
-    def << string
-      if string.encoding == BINARY
-        super(string)
-      else
-        super(string.b)
+  if String.method_defined?(:append_as_bytes)
+    Buffer = String
+  else
+    class Buffer < String
+      def append_as_bytes(string)
+        if string.encoding == Encoding::BINARY || string.ascii_only?
+          self << string
+        else
+          self << string.b
+        end
       end
-
-      return self
     end
-
-    alias concat <<
   end
 
   ##
@@ -352,22 +344,32 @@ def eof?
 
   def do_write(s)
     @wbuffer = Buffer.new unless defined? @wbuffer
-    @wbuffer << s
-    @wbuffer.force_encoding(Encoding::BINARY)
+    @wbuffer.append_as_bytes(s)
+
     @sync ||= false
-    buffer_size = @wbuffer.size
+    buffer_size = @wbuffer.bytesize
     if @sync or buffer_size > BLOCK_SIZE
       nwrote = 0
       begin
         while nwrote < buffer_size do
           begin
-            nwrote += syswrite(@wbuffer[nwrote, buffer_size - nwrote])
+            chunk = if nwrote > 0
+              @wbuffer.byteslice(nwrote..-1)
+            else
+              @wbuffer
+            end
+
+            nwrote += syswrite(chunk)
           rescue Errno::EAGAIN
             retry
           end
         end
       ensure
-        @wbuffer[0, nwrote] = ""
+        if nwrote < @wbuffer.bytesize
+          @wbuffer[0, nwrote] = ""
+        else
+          @wbuffer.clear
+        end
       end
     end
   end