diff --git a/diff.c b/diff.c
index fc3cc73..7da16c9 100644
--- a/diff.c
+++ b/diff.c
@@ -3544,9 +3544,9 @@
 	else if (!strcmp(arg, "--ignore-space-at-eol"))
 		DIFF_XDL_SET(options, IGNORE_WHITESPACE_AT_EOL);
 	else if (!strcmp(arg, "--patience"))
-		DIFF_XDL_SET(options, PATIENCE_DIFF);
+		options->xdl_opts = DIFF_WITH_ALG(options, PATIENCE_DIFF);
 	else if (!strcmp(arg, "--histogram"))
-		DIFF_XDL_SET(options, HISTOGRAM_DIFF);
+		options->xdl_opts = DIFF_WITH_ALG(options, HISTOGRAM_DIFF);
 
 	/* flags options */
 	else if (!strcmp(arg, "--binary")) {
diff --git a/diff.h b/diff.h
index 3cc1dcf..e027650 100644
--- a/diff.h
+++ b/diff.h
@@ -91,6 +91,8 @@
 #define DIFF_XDL_SET(opts, flag)    ((opts)->xdl_opts |= XDF_##flag)
 #define DIFF_XDL_CLR(opts, flag)    ((opts)->xdl_opts &= ~XDF_##flag)
 
+#define DIFF_WITH_ALG(opts, flag)   (((opts)->xdl_opts & ~XDF_DIFF_ALGORITHM_MASK) | XDF_##flag)
+
 enum diff_words_type {
 	DIFF_WORDS_NONE = 0,
 	DIFF_WORDS_PORCELAIN,
diff --git a/merge-recursive.c b/merge-recursive.c
index 0fb1743..680937c 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -2069,9 +2069,9 @@
 	else if (!prefixcmp(s, "subtree="))
 		o->subtree_shift = s + strlen("subtree=");
 	else if (!strcmp(s, "patience"))
-		o->xdl_opts |= XDF_PATIENCE_DIFF;
+		o->xdl_opts = DIFF_WITH_ALG(o, PATIENCE_DIFF);
 	else if (!strcmp(s, "histogram"))
-		o->xdl_opts |= XDF_HISTOGRAM_DIFF;
+		o->xdl_opts = DIFF_WITH_ALG(o, HISTOGRAM_DIFF);
 	else if (!strcmp(s, "ignore-space-change"))
 		o->xdl_opts |= XDF_IGNORE_WHITESPACE_CHANGE;
 	else if (!strcmp(s, "ignore-all-space"))
diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
index 00d36c3..09215af 100644
--- a/xdiff/xdiff.h
+++ b/xdiff/xdiff.h
@@ -32,14 +32,12 @@
 #define XDF_IGNORE_WHITESPACE (1 << 2)
 #define XDF_IGNORE_WHITESPACE_CHANGE (1 << 3)
 #define XDF_IGNORE_WHITESPACE_AT_EOL (1 << 4)
-#define XDF_PATIENCE_DIFF (1 << 5)
-#define XDF_HISTOGRAM_DIFF (1 << 6)
 #define XDF_WHITESPACE_FLAGS (XDF_IGNORE_WHITESPACE | XDF_IGNORE_WHITESPACE_CHANGE | XDF_IGNORE_WHITESPACE_AT_EOL)
 
-#define XDL_PATCH_NORMAL '-'
-#define XDL_PATCH_REVERSE '+'
-#define XDL_PATCH_MODEMASK ((1 << 8) - 1)
-#define XDL_PATCH_IGNOREBSPACE (1 << 8)
+#define XDF_PATIENCE_DIFF (1 << 5)
+#define XDF_HISTOGRAM_DIFF (1 << 6)
+#define XDF_DIFF_ALGORITHM_MASK (XDF_PATIENCE_DIFF | XDF_HISTOGRAM_DIFF)
+#define XDF_DIFF_ALG(x) ((x) & XDF_DIFF_ALGORITHM_MASK)
 
 #define XDL_EMIT_FUNCNAMES (1 << 0)
 #define XDL_EMIT_COMMON (1 << 1)
diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
index 75a3922..bc889e8 100644
--- a/xdiff/xdiffi.c
+++ b/xdiff/xdiffi.c
@@ -328,10 +328,10 @@
 	xdalgoenv_t xenv;
 	diffdata_t dd1, dd2;
 
-	if (xpp->flags & XDF_PATIENCE_DIFF)
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF)
 		return xdl_do_patience_diff(mf1, mf2, xpp, xe);
 
-	if (xpp->flags & XDF_HISTOGRAM_DIFF)
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
 		return xdl_do_histogram_diff(mf1, mf2, xpp, xe);
 
 	if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0) {
diff --git a/xdiff/xhistogram.c b/xdiff/xhistogram.c
index 18f6f99..bf99787 100644
--- a/xdiff/xhistogram.c
+++ b/xdiff/xhistogram.c
@@ -252,7 +252,7 @@
 		int line1, int count1, int line2, int count2)
 {
 	xpparam_t xpp;
-	xpp.flags = index->xpp->flags & ~XDF_HISTOGRAM_DIFF;
+	xpp.flags = index->xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
 
 	return xdl_fall_back_diff(index->env, &xpp,
 				  line1, count1, line2, count2);
diff --git a/xdiff/xpatience.c b/xdiff/xpatience.c
index fdd7d02..04e1a1a 100644
--- a/xdiff/xpatience.c
+++ b/xdiff/xpatience.c
@@ -288,7 +288,7 @@
 		int line1, int count1, int line2, int count2)
 {
 	xpparam_t xpp;
-	xpp.flags = map->xpp->flags & ~XDF_PATIENCE_DIFF;
+	xpp.flags = map->xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
 
 	return xdl_fall_back_diff(map->env, &xpp,
 				  line1, count1, line2, count2);
diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index e419f4f..63a22c6 100644
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -181,7 +181,7 @@
 	if (!(recs = (xrecord_t **) xdl_malloc(narec * sizeof(xrecord_t *))))
 		goto abort;
 
-	if (xpp->flags & XDF_HISTOGRAM_DIFF)
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
 		hbits = hsize = 0;
 	else {
 		hbits = xdl_hashbits((unsigned int) narec);
@@ -209,8 +209,8 @@
 			crec->ha = hav;
 			recs[nrec++] = crec;
 
-			if (!(xpp->flags & XDF_HISTOGRAM_DIFF) &&
-				xdl_classify_record(pass, cf, rhash, hbits, crec) < 0)
+			if ((XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+			    xdl_classify_record(pass, cf, rhash, hbits, crec) < 0)
 				goto abort;
 		}
 	}
@@ -273,16 +273,15 @@
 	 * (nrecs) will be updated correctly anyway by
 	 * xdl_prepare_ctx().
 	 */
-	sample = xpp->flags & XDF_HISTOGRAM_DIFF ? XDL_GUESS_NLINES2 : XDL_GUESS_NLINES1;
+	sample = (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF
+		  ? XDL_GUESS_NLINES2 : XDL_GUESS_NLINES1);
 
 	enl1 = xdl_guess_lines(mf1, sample) + 1;
 	enl2 = xdl_guess_lines(mf2, sample) + 1;
 
-	if (!(xpp->flags & XDF_HISTOGRAM_DIFF) &&
-		xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0) {
-
+	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF &&
+	    xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0)
 		return -1;
-	}
 
 	if (xdl_prepare_ctx(1, mf1, enl1, xpp, &cf, &xe->xdf1) < 0) {
 
@@ -296,9 +295,9 @@
 		return -1;
 	}
 
-	if (!(xpp->flags & XDF_PATIENCE_DIFF) &&
-			!(xpp->flags & XDF_HISTOGRAM_DIFF) &&
-			xdl_optimize_ctxs(&cf, &xe->xdf1, &xe->xdf2) < 0) {
+	if ((XDF_DIFF_ALG(xpp->flags) != XDF_PATIENCE_DIFF) &&
+	    (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+	    xdl_optimize_ctxs(&cf, &xe->xdf1, &xe->xdf2) < 0) {
 
 		xdl_free_ctx(&xe->xdf2);
 		xdl_free_ctx(&xe->xdf1);