diff --git a/src/liblzma/delta/Makefile.am b/src/liblzma/delta/Makefile.am
index fc09f5b8..899d9bc0 100644
--- a/src/liblzma/delta/Makefile.am
+++ b/src/liblzma/delta/Makefile.am
@@ -19,7 +19,8 @@ libdelta_la_CPPFLAGS = \
 
 libdelta_la_SOURCES = \
 	delta_common.c \
-	delta_common.h
+	delta_common.h \
+	delta_private.h
 
 if COND_ENCODER_DELTA
 libdelta_la_SOURCES += \
diff --git a/src/liblzma/delta/delta_common.c b/src/liblzma/delta/delta_common.c
index 90b5552b..ee2abd65 100644
--- a/src/liblzma/delta/delta_common.c
+++ b/src/liblzma/delta/delta_common.c
@@ -18,6 +18,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "delta_common.h"
+#include "delta_private.h"
 
 
 static void
@@ -47,15 +48,14 @@ lzma_delta_coder_init(lzma_next_coder *next, lzma_allocator *allocator,
 	// Coding function is different for encoder and decoder.
 	next->code = code;
 
-	// Set the delta distance.
-	if (filters[0].options == NULL)
-		return LZMA_PROG_ERROR;
-	next->coder->distance
-			= ((lzma_options_delta *)(filters[0].options))->dist;
-	if (next->coder->distance < LZMA_DELTA_DIST_MIN
-			|| next->coder->distance > LZMA_DELTA_DIST_MAX)
+	// Validate the options.
+	if (lzma_delta_coder_memusage(filters[0].options) == UINT64_MAX)
 		return LZMA_OPTIONS_ERROR;
 
+	// Set the delta distance.
+	const lzma_options_delta *opt = filters[0].options;
+	next->coder->distance = opt->dist;
+
 	// Initialize the rest of the variables.
 	next->coder->pos = 0;
 	memzero(next->coder->history, LZMA_DELTA_DIST_MAX);
@@ -64,3 +64,17 @@ lzma_delta_coder_init(lzma_next_coder *next, lzma_allocator *allocator,
 	return lzma_next_filter_init(&next->coder->next,
 			allocator, filters + 1);
 }
+
+
+extern uint64_t
+lzma_delta_coder_memusage(const void *options)
+{
+	const lzma_options_delta *opt = options;
+
+	if (opt == NULL || opt->type != LZMA_DELTA_TYPE_BYTE
+			|| opt->dist < LZMA_DELTA_DIST_MIN
+			|| opt->dist > LZMA_DELTA_DIST_MAX)
+		return UINT64_MAX;
+
+	return sizeof(lzma_coder);
+}
diff --git a/src/liblzma/delta/delta_common.h b/src/liblzma/delta/delta_common.h
index e7b3eeda..a01de547 100644
--- a/src/liblzma/delta/delta_common.h
+++ b/src/liblzma/delta/delta_common.h
@@ -22,23 +22,6 @@
 
 #include "common.h"
 
-struct lzma_coder_s {
-	/// Next coder in the chain
-	lzma_next_coder next;
-
-	/// Delta distance
-	size_t distance;
-
-	/// Position in history[]
-	uint8_t pos;
-
-	/// Buffer to hold history of the original data
-	uint8_t history[LZMA_DELTA_DIST_MAX];
-};
-
-
-extern lzma_ret lzma_delta_coder_init(
-		lzma_next_coder *next, lzma_allocator *allocator,
-		const lzma_filter_info *filters, lzma_code_function code);
+extern uint64_t lzma_delta_coder_memusage(const void *options);
 
 #endif
diff --git a/src/liblzma/delta/delta_decoder.c b/src/liblzma/delta/delta_decoder.c
index 26dc40fe..0211a38a 100644
--- a/src/liblzma/delta/delta_decoder.c
+++ b/src/liblzma/delta/delta_decoder.c
@@ -18,7 +18,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "delta_decoder.h"
-#include "delta_common.h"
+#include "delta_private.h"
 
 
 static void
diff --git a/src/liblzma/delta/delta_decoder.h b/src/liblzma/delta/delta_decoder.h
index 84852bf3..7a71feae 100644
--- a/src/liblzma/delta/delta_decoder.h
+++ b/src/liblzma/delta/delta_decoder.h
@@ -20,7 +20,7 @@
 #ifndef LZMA_DELTA_DECODER_H
 #define LZMA_DELTA_DECODER_H
 
-#include "common.h"
+#include "delta_common.h"
 
 extern lzma_ret lzma_delta_decoder_init(lzma_next_coder *next,
 		lzma_allocator *allocator, const lzma_filter_info *filters);
diff --git a/src/liblzma/delta/delta_encoder.c b/src/liblzma/delta/delta_encoder.c
index bb772a6c..751aa92d 100644
--- a/src/liblzma/delta/delta_encoder.c
+++ b/src/liblzma/delta/delta_encoder.c
@@ -18,7 +18,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "delta_encoder.h"
-#include "delta_common.h"
+#include "delta_private.h"
 
 
 /// Copies and encodes the data at the same time. This is used when Delta
@@ -101,18 +101,12 @@ lzma_delta_encoder_init(lzma_next_coder *next, lzma_allocator *allocator,
 extern lzma_ret
 lzma_delta_props_encode(const void *options, uint8_t *out)
 {
-	if (options == NULL)
+	// The caller must have already validated the options, so it's
+	// LZMA_PROG_ERROR if they are invalid.
+	if (lzma_delta_coder_memusage(options) == UINT64_MAX)
 		return LZMA_PROG_ERROR;
 
 	const lzma_options_delta *opt = options;
-
-	// It's possible that newer liblzma versions will support larger
-	// distance values.
-	if (opt->type != LZMA_DELTA_TYPE_BYTE
-			|| opt->dist < LZMA_DELTA_DIST_MIN
-			|| opt->dist > LZMA_DELTA_DIST_MAX)
-		return LZMA_OPTIONS_ERROR;
-
 	out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
 
 	return LZMA_OK;
diff --git a/src/liblzma/delta/delta_encoder.h b/src/liblzma/delta/delta_encoder.h
index b8b29c61..a709d1ca 100644
--- a/src/liblzma/delta/delta_encoder.h
+++ b/src/liblzma/delta/delta_encoder.h
@@ -20,7 +20,7 @@
 #ifndef LZMA_DELTA_ENCODER_H
 #define LZMA_DELTA_ENCODER_H
 
-#include "common.h"
+#include "delta_common.h"
 
 extern lzma_ret lzma_delta_encoder_init(lzma_next_coder *next,
 		lzma_allocator *allocator, const lzma_filter_info *filters);
diff --git a/src/liblzma/delta/delta_private.h b/src/liblzma/delta/delta_private.h
new file mode 100644
index 00000000..e1d59340
--- /dev/null
+++ b/src/liblzma/delta/delta_private.h
@@ -0,0 +1,44 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       delta_private.h
+/// \brief      Private common stuff for Delta encoder and decoder
+//
+//  Copyright (C) 2007 Lasse Collin
+//
+//  This library is free software; you can redistribute it and/or
+//  modify it under the terms of the GNU Lesser General Public
+//  License as published by the Free Software Foundation; either
+//  version 2.1 of the License, or (at your option) any later version.
+//
+//  This library is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+//  Lesser General Public License for more details.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef LZMA_DELTA_PRIVATE_H
+#define LZMA_DELTA_PRIVATE_H
+
+#include "delta_common.h"
+
+struct lzma_coder_s {
+	/// Next coder in the chain
+	lzma_next_coder next;
+
+	/// Delta distance
+	size_t distance;
+
+	/// Position in history[]
+	uint8_t pos;
+
+	/// Buffer to hold history of the original data
+	uint8_t history[LZMA_DELTA_DIST_MAX];
+};
+
+
+extern lzma_ret lzma_delta_coder_init(
+		lzma_next_coder *next, lzma_allocator *allocator,
+		const lzma_filter_info *filters, lzma_code_function code);
+
+#endif