diff --git a/builtin/merge-file.c b/builtin/merge-file.c
index 06a2f90c48..e695867ee5 100644
--- a/builtin/merge-file.c
+++ b/builtin/merge-file.c
@@ -34,6 +34,8 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 	struct option options[] = {
 		OPT_BOOL('p', "stdout", &to_stdout, N_("send results to standard output")),
 		OPT_SET_INT(0, "diff3", &xmp.style, N_("use a diff3 based merge"), XDL_MERGE_DIFF3),
+		OPT_SET_INT(0, "zdiff3", &xmp.style, N_("use a zealous diff3 based merge"),
+				XDL_MERGE_ZEALOUS_DIFF3),
 		OPT_SET_INT(0, "ours", &xmp.favor, N_("for conflicts, use our version"),
 			    XDL_MERGE_FAVOR_OURS),
 		OPT_SET_INT(0, "theirs", &xmp.favor, N_("for conflicts, use their version"),
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index c82ccaebcc..3bfb4c8892 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1566,7 +1566,7 @@ _git_checkout ()
 
 	case "$cur" in
 	--conflict=*)
-		__gitcomp "diff3 merge" "" "${cur##--conflict=}"
+		__gitcomp "diff3 merge zdiff3" "" "${cur##--conflict=}"
 		;;
 	--*)
 		__gitcomp_builtin checkout
@@ -2437,7 +2437,7 @@ _git_switch ()
 
 	case "$cur" in
 	--conflict=*)
-		__gitcomp "diff3 merge" "" "${cur##--conflict=}"
+		__gitcomp "diff3 merge zdiff3" "" "${cur##--conflict=}"
 		;;
 	--*)
 		__gitcomp_builtin switch
@@ -2877,7 +2877,7 @@ _git_restore ()
 
 	case "$cur" in
 	--conflict=*)
-		__gitcomp "diff3 merge" "" "${cur##--conflict=}"
+		__gitcomp "diff3 merge zdiff3" "" "${cur##--conflict=}"
 		;;
 	--source=*)
 		__git_complete_refs --cur="${cur##--source=}"
diff --git a/t/t6427-diff3-conflict-markers.sh b/t/t6427-diff3-conflict-markers.sh
index 25c4b720e7..a9ee4cb207 100755
--- a/t/t6427-diff3-conflict-markers.sh
+++ b/t/t6427-diff3-conflict-markers.sh
@@ -211,4 +211,94 @@ test_expect_success 'rebase --apply describes fake ancestor base' '
 	)
 '
 
+test_setup_zdiff3 () {
+	test_create_repo zdiff3 &&
+	(
+		cd zdiff3 &&
+
+		test_write_lines 1 2 3 4 5 6 7 8 9 >basic &&
+		test_write_lines 1 2 3 AA 4 5 BB 6 7 8 >middle-common &&
+		test_write_lines 1 2 3 4 5 6 7 8 9 >interesting &&
+		test_write_lines 1 2 3 4 5 6 7 8 9 >evil &&
+
+		git add basic middle-common interesting evil &&
+		git commit -m base &&
+
+		git branch left &&
+		git branch right &&
+
+		git checkout left &&
+		test_write_lines 1 2 3 4 A B C D E 7 8 9 >basic &&
+		test_write_lines 1 2 3 CC 4 5 DD 6 7 8 >middle-common &&
+		test_write_lines 1 2 3 4 A B C D E F G H I J 7 8 9 >interesting &&
+		test_write_lines 1 2 3 4 X A B C 7 8 9 >evil &&
+		git add -u &&
+		git commit -m letters &&
+
+		git checkout right &&
+		test_write_lines 1 2 3 4 A X C Y E 7 8 9 >basic &&
+		test_write_lines 1 2 3 EE 4 5 FF 6 7 8 >middle-common &&
+		test_write_lines 1 2 3 4 A B C 5 6 G H I J 7 8 9 >interesting &&
+		test_write_lines 1 2 3 4 Y A B C B C 7 8 9 >evil &&
+		git add -u &&
+		git commit -m permuted
+	)
+}
+
+test_expect_success 'check zdiff3 markers' '
+	test_setup_zdiff3 &&
+	(
+		cd zdiff3 &&
+
+		git checkout left^0 &&
+
+		base=$(git rev-parse --short HEAD^1) &&
+		test_must_fail git -c merge.conflictstyle=zdiff3 merge -s recursive right^0 &&
+
+		test_write_lines 1 2 3 4 A \
+				 "<<<<<<< HEAD" B C D \
+				 "||||||| $base" 5 6 \
+				 ======= X C Y \
+				 ">>>>>>> right^0" \
+				 E 7 8 9 \
+				 >expect &&
+		test_cmp expect basic &&
+
+		test_write_lines 1 2 3 \
+				 "<<<<<<< HEAD" CC \
+				 "||||||| $base" AA \
+				 ======= EE \
+				 ">>>>>>> right^0" \
+				 4 5 \
+				 "<<<<<<< HEAD" DD \
+				 "||||||| $base" BB \
+				 ======= FF \
+				 ">>>>>>> right^0" \
+				 6 7 8 \
+				 >expect &&
+		test_cmp expect middle-common &&
+
+		test_write_lines 1 2 3 4 A B C \
+				 "<<<<<<< HEAD" D E F \
+				 "||||||| $base" 5 6 \
+				 ======= 5 6 \
+				 ">>>>>>> right^0" \
+				 G H I J 7 8 9 \
+				 >expect &&
+		test_cmp expect interesting &&
+
+		# Not passing this one yet; the common "B C" lines is still
+		# being left in the conflict blocks on the left and right
+		# sides.
+		test_write_lines 1 2 3 4 \
+				 "<<<<<<< HEAD" X A \
+				 "||||||| $base" 5 6 \
+				 ======= Y A B C \
+				 ">>>>>>> right^0" \
+				 B C 7 8 9 \
+				 >expect &&
+		test_cmp expect evil
+	)
+'
+
 test_done
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 75b32aef51..2e3a5a2943 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -313,6 +313,8 @@ int git_xmerge_config(const char *var, const char *value, void *cb)
 			die("'%s' is not a boolean", var);
 		if (!strcmp(value, "diff3"))
 			git_xmerge_style = XDL_MERGE_DIFF3;
+		else if (!strcmp(value, "zdiff3"))
+			git_xmerge_style = XDL_MERGE_ZEALOUS_DIFF3;
 		else if (!strcmp(value, "merge"))
 			git_xmerge_style = 0;
 		/*
diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
index b29deca5de..72e25a9ffa 100644
--- a/xdiff/xdiff.h
+++ b/xdiff/xdiff.h
@@ -66,6 +66,7 @@ extern "C" {
 
 /* merge output styles */
 #define XDL_MERGE_DIFF3 1
+#define XDL_MERGE_ZEALOUS_DIFF3 2
 
 typedef struct s_mmfile {
 	char *ptr;
diff --git a/xdiff/xmerge.c b/xdiff/xmerge.c
index 1659edb453..fff0b594f9 100644
--- a/xdiff/xmerge.c
+++ b/xdiff/xmerge.c
@@ -230,7 +230,7 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 	size += xdl_recs_copy(xe1, m->i1, m->chg1, needs_cr, 1,
 			      dest ? dest + size : NULL);
 
-	if (style == XDL_MERGE_DIFF3) {
+	if (style == XDL_MERGE_DIFF3 || style == XDL_MERGE_ZEALOUS_DIFF3) {
 		/* Shared preimage */
 		if (!dest) {
 			size += marker_size + 1 + needs_cr + marker3_size;
@@ -322,6 +322,40 @@ static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
 	return size;
 }
 
+static int recmatch(xrecord_t *rec1, xrecord_t *rec2, unsigned long flags)
+{
+	return xdl_recmatch(rec1->ptr, rec1->size,
+			    rec2->ptr, rec2->size, flags);
+}
+
+/*
+ * Remove any common lines from the beginning and end of the conflicted region.
+ */
+static void xdl_refine_zdiff3_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
+		xpparam_t const *xpp)
+{
+	xrecord_t **rec1 = xe1->xdf2.recs, **rec2 = xe2->xdf2.recs;
+	for (; m; m = m->next) {
+		/* let's handle just the conflicts */
+		if (m->mode)
+			continue;
+
+		while(m->chg1 && m->chg2 &&
+		      recmatch(rec1[m->i1], rec2[m->i2], xpp->flags)) {
+			m->chg1--;
+			m->chg2--;
+			m->i1++;
+			m->i2++;
+		}
+		while (m->chg1 && m->chg2 &&
+		       recmatch(rec1[m->i1 + m->chg1 - 1],
+				rec2[m->i2 + m->chg2 - 1], xpp->flags)) {
+			m->chg1--;
+			m->chg2--;
+		}
+	}
+}
+
 /*
  * Sometimes, changes are not quite identical, but differ in only a few
  * lines. Try hard to show only these few lines as conflicting.
@@ -482,7 +516,22 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
 	int style = xmp->style;
 	int favor = xmp->favor;
 
-	if (style == XDL_MERGE_DIFF3) {
+	/*
+	 * XDL_MERGE_DIFF3 does not attempt to refine conflicts by looking
+	 * at common areas of sides 1 & 2, because the base (side 0) does
+	 * not match and is being shown.  Similarly, simplification of
+	 * non-conflicts is also skipped due to the skipping of conflict
+	 * refinement.
+	 *
+	 * XDL_MERGE_ZEALOUS_DIFF3, on the other hand, will attempt to
+	 * refine conflicts looking for common areas of sides 1 & 2.
+	 * However, since the base is being shown and does not match,
+	 * it will only look for common areas at the beginning or end
+	 * of the conflict block.  Since XDL_MERGE_ZEALOUS_DIFF3's
+	 * conflict refinement is much more limited in this fashion, the
+	 * conflict simplification will be skipped.
+	 */
+	if (style == XDL_MERGE_DIFF3 || style == XDL_MERGE_ZEALOUS_DIFF3) {
 		/*
 		 * "diff3 -m" output does not make sense for anything
 		 * more aggressive than XDL_MERGE_EAGER.
@@ -603,10 +652,12 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
 	if (!changes)
 		changes = c;
 	/* refine conflicts */
-	if (XDL_MERGE_ZEALOUS <= level &&
-	    (xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
-	     xdl_simplify_non_conflicts(xe1, changes,
-					XDL_MERGE_ZEALOUS < level) < 0)) {
+	if (style == XDL_MERGE_ZEALOUS_DIFF3) {
+		xdl_refine_zdiff3_conflicts(xe1, xe2, changes, xpp);
+	} else if (XDL_MERGE_ZEALOUS <= level &&
+		   (xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
+		    xdl_simplify_non_conflicts(xe1, changes,
+					       XDL_MERGE_ZEALOUS < level) < 0)) {
 		xdl_cleanup_merge(changes);
 		return -1;
 	}