diff --git a/src/CHANGELOG b/src/CHANGELOG
index 248ed655f..bffae4dae 100644
--- a/src/CHANGELOG
+++ b/src/CHANGELOG
@@ -25,9 +25,9 @@ ECL 9.1.0:
    as a base-string.
 
  - ECL supports external formats. They may be a symbol, denoting the encoding
-   or an encoding option, or a list of symbols. Valid symbols are :DEFAULT,
-   :LATIN-1, :ISO-8859-1, :UTF-8, :UCS-{2,4}{,BE,LE} :CR, :LF and :CRLF. Default
-   option is :LF.
+   or an encoding option, an association table between bytes and unicode codes
+   or a list of these. Valid symbols are :DEFAULT, :LATIN-1, :ISO-8859-1,
+   :UTF-8, :UCS-{2,4}{,BE,LE} :CR, :LF and :CRLF. Default option is :LF.
 
 * Bugs fixed:
 
diff --git a/src/c/file.d b/src/c/file.d
index 75e433fef..77ed3173a 100644
--- a/src/c/file.d
+++ b/src/c/file.d
@@ -725,6 +725,56 @@ ucs_2_encoder(cl_object stream, unsigned char *buffer, int c)
 	return 2 + ucs_2be_encoder(stream, buffer+2, c);
 }
 
+/*
+ * UCS-2 BOM ENDIAN
+ */
+
+static int
+user_decoder(cl_object stream, cl_eformat_read_byte8 read_byte8, cl_object source)
+{
+	cl_object table = stream->stream.format_table;
+	cl_object character, byte;
+	unsigned char buffer[2];
+	if (read_byte8(source, buffer, 1) < 1) {
+		return EOF;
+	}
+	byte = MAKE_FIXNUM(buffer);
+	character = ecl_gethash_safe(MAKE_FIXNUM(buffer[0]), table, Cnil);
+	if (Null(character)) {
+		return EOF-2;
+	}
+	if (character == Ct) {
+		if (read_byte8(source, buffer+1, 1) < 1) {
+			return EOF;
+		}
+		character = ecl_gethash_safe(MAKE_FIXNUM((buffer[0]<<8+buffer[1])),
+					     table, Cnil);
+		if (Null(character)) {
+			return EOF-2;
+		}
+	}
+	return CHAR_CODE(character);
+}
+
+static int
+user_encoder(cl_object stream, unsigned char *buffer, int c)
+{
+	cl_object byte = ecl_gethash_safe(CODE_CHAR(c), stream->stream.format_table, Cnil);
+	if (Null(byte)) {
+		return 0;
+	} else {
+		cl_fixnum code = fix(byte);
+		if (c > 0xFF) {
+			buffer[1] = c & 8; c >>= 8;
+			buffer[0] = c;
+			return 2;
+		} else {
+			buffer[0] = c;
+			return 1;
+		}
+	}
+}
+
 /*
  * UTF-8
  */
@@ -2519,15 +2569,14 @@ const struct ecl_file_ops input_file_ops = {
 
 
 static int
-parse_external_format(cl_object strm, cl_object format)
+parse_external_format(cl_object stream, cl_object format)
 {
 	if (CONSP(format)) {
 		int flags = 0;
 		do {
-			flags |= parse_external_format(strm, ECL_CONS_CAR(format));
+			flags |= parse_external_format(stream, ECL_CONS_CAR(format));
 			format = cl_cdr(format);
 		} while (CONSP(format));
-		printf("%d\n", flags);
 		return flags;
 	}
 	if (FIXNUMP(format)) {
@@ -2582,6 +2631,10 @@ parse_external_format(cl_object strm, cl_object format)
 		/* Binary stream */
 		return 0;
 	}
+	if (type_of(format) == t_hashtable) {
+		stream->stream.format_table = format;
+		return ECL_STREAM_USER_FORMAT;
+	}
 	FEerror("Unknown external format: ~A", 1, format);
 	return ECL_STREAM_DEFAULT_FORMAT;
 }
@@ -2668,6 +2721,13 @@ set_stream_elt_type(cl_object stream, cl_fixnum byte_size, int flags,
 		stream->stream.decoder = ucs_4le_decoder;
 		break;
 #endif
+	case ECL_STREAM_USER_FORMAT:
+		IO_STREAM_ELT_TYPE(stream) = @'character';
+		byte_size = 8;
+		stream->stream.format = stream->stream.format_table;
+		stream->stream.encoder = user_encoder;
+		stream->stream.decoder = user_decoder;
+		break;
 	default:
 		FEerror("Invalid external format code ~D with ~A",
 			1, MAKE_FIXNUM(flags), external_format);
diff --git a/src/h/object.h b/src/h/object.h
index dca9d6bf0..7720003f4 100644
--- a/src/h/object.h
+++ b/src/h/object.h
@@ -526,12 +526,12 @@ enum {
 	ECL_STREAM_UCS_4 = 6,
 	ECL_STREAM_UCS_4LE = 7,
 	ECL_STREAM_UCS_4BE = 8,
-	ECL_STREAM_8BIT = 5,
-	ECL_STREAM_CR = 8,
-	ECL_STREAM_LF = 16,
-	ECL_STREAM_SIGNED_BYTES = 32,
-	ECL_STREAM_C_STREAM = 64,
-	ECL_STREAM_MIGHT_SEEK = 128
+	ECL_STREAM_USER_FORMAT = 9,
+	ECL_STREAM_CR = 16,
+	ECL_STREAM_LF = 32,
+	ECL_STREAM_SIGNED_BYTES = 64,
+	ECL_STREAM_C_STREAM = 128,
+	ECL_STREAM_MIGHT_SEEK = 256
 };
 
 typedef int (*cl_eformat_encoder)(cl_object stream, unsigned char *buffer, int c);
@@ -556,8 +556,7 @@ struct ecl_stream {
 	cl_object format;	/*  external format  */
 	cl_eformat_encoder encoder;
 	cl_eformat_decoder decoder;
-	cl_object encoder_table;
-	cl_object decoder_table;
+	cl_object format_table;
 	int flags;		/*  character table, flags, etc  */
 };
 
diff --git a/src/lsp/iolib.lsp b/src/lsp/iolib.lsp
index 29b6be26f..a91257491 100644
--- a/src/lsp/iolib.lsp
+++ b/src/lsp/iolib.lsp
@@ -287,3 +287,24 @@ the one defined in the ANSI standard. *print-base* is 10, *print-array* is t,
 	 (print-unreadable-object-function
 	   ,object ,stream ,type ,identity #'.print-unreadable-object-body.))
     `(print-unreadable-object-function ,object ,stream ,type ,identity nil)))
+
+(defun ext::load-encoding (name)
+  (let ((filename (make-pathname :name (symbol-name name) :defaults "SYS:encodings;")))
+    (print name)
+    (unless (probe-file filename)
+      (error "Unable to find mapping file ~A for encoding ~A" filename name))
+    (with-open-file (s filename :direction :input)
+      (read s))))
+
+(defun ext::make-encoding (mapping)
+  (when (symbolp mapping)
+    (setf mapping (load-encoding mapping)))
+  (let ((output (make-hash-table :size 512 :test 'eq)))
+    (dolist (record mapping output)
+      (let* ((byte (car record))
+	     (unicode (cdr record))
+	     (unicode-char (code-char unicode)))
+	(when (> byte #xFF)
+	  (setf (gethash (ash byte -8) output) t))
+	(setf (gethash byte output) unicode-char)
+	(setf (gethash unicode-char output) byte)))))