diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 530d1159141..32e6dee5ac3 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -49,10 +49,9 @@ ifdef::git-log[]
 --diff-merges=m:::
 -m:::
 	This option makes diff output for merge commits to be shown in
-	the default format. `-m` will produce the output only if `-p`
-	is given as well. The default format could be changed using
+	the default format. The default format could be changed using
 	`log.diffMerges` configuration parameter, which default value
-	is `separate`.
+	is `separate`. `-m` implies `-p`.
 +
 --diff-merges=first-parent:::
 --diff-merges=1:::
@@ -62,7 +61,8 @@ ifdef::git-log[]
 --diff-merges=separate:::
 	This makes merge commits show the full diff with respect to
 	each of the parents. Separate log entry and diff is generated
-	for each parent.
+	for each parent. This is the format that `-m` produced
+	historically.
 +
 --diff-merges=combined:::
 --diff-merges=c:::
diff --git a/builtin/diff-index.c b/builtin/diff-index.c
index 176fe7ff2b4..cf09559e422 100644
--- a/builtin/diff-index.c
+++ b/builtin/diff-index.c
@@ -2,6 +2,7 @@
 #include "cache.h"
 #include "config.h"
 #include "diff.h"
+#include "diff-merges.h"
 #include "commit.h"
 #include "revision.h"
 #include "builtin.h"
@@ -27,6 +28,12 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 	rev.abbrev = 0;
 	prefix = precompose_argv_prefix(argc, argv, prefix);
 
+	/*
+	 * We need no diff for merges options, and we need to avoid conflict
+	 * with our own meaning of "-m".
+	 */
+	diff_merges_suppress_options_parsing();
+
 	argc = setup_revisions(argc, argv, &rev, NULL);
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
@@ -35,6 +42,8 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 			option |= DIFF_INDEX_CACHED;
 		else if (!strcmp(arg, "--merge-base"))
 			option |= DIFF_INDEX_MERGE_BASE;
+		else if (!strcmp(arg, "-m"))
+			rev.match_missing = 1;
 		else
 			usage(diff_cache_usage);
 	}
diff --git a/builtin/stash.c b/builtin/stash.c
index d163fb66d2c..9c72e4b1257 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -761,7 +761,7 @@ static int list_stash(int argc, const char **argv, const char *prefix)
 
 	cp.git_cmd = 1;
 	strvec_pushl(&cp.args, "log", "--format=%gd: %gs", "-g",
-		     "--first-parent", "-m", NULL);
+		     "--first-parent", NULL);
 	strvec_pushv(&cp.args, argv);
 	strvec_push(&cp.args, ref_stash);
 	strvec_push(&cp.args, "--");
diff --git a/diff-merges.c b/diff-merges.c
index f3a9daed7e0..0dfcaa1b11b 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -6,6 +6,7 @@ typedef void (*diff_merges_setup_func_t)(struct rev_info *);
 static void set_separate(struct rev_info *revs);
 
 static diff_merges_setup_func_t set_to_default = set_separate;
+static int suppress_parsing;
 
 static void suppress(struct rev_info *revs)
 {
@@ -14,7 +15,7 @@ static void suppress(struct rev_info *revs)
 	revs->combine_merges = 0;
 	revs->dense_combined_merges = 0;
 	revs->combined_all_paths = 0;
-	revs->combined_imply_patch = 0;
+	revs->merges_imply_patch = 0;
 	revs->merges_need_diff = 0;
 }
 
@@ -30,17 +31,6 @@ static void set_first_parent(struct rev_info *revs)
 	revs->first_parent_merges = 1;
 }
 
-static void set_m(struct rev_info *revs)
-{
-	/*
-	 * To "diff-index", "-m" means "match missing", and to the "log"
-	 * family of commands, it means "show default diff for merges". Set
-	 * both fields appropriately.
-	 */
-	set_to_default(revs);
-	revs->match_missing = 1;
-}
-
 static void set_combined(struct rev_info *revs)
 {
 	suppress(revs);
@@ -101,20 +91,29 @@ int diff_merges_config(const char *value)
 	return 0;
 }
 
+void diff_merges_suppress_options_parsing(void)
+{
+	suppress_parsing = 1;
+}
+
 int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 {
 	int argcount = 1;
 	const char *optarg;
 	const char *arg = argv[0];
 
+	if (suppress_parsing)
+		return 0;
+
 	if (!strcmp(arg, "-m")) {
-		set_m(revs);
+		set_to_default(revs);
+		revs->merges_imply_patch = 1;
 	} else if (!strcmp(arg, "-c")) {
 		set_combined(revs);
-		revs->combined_imply_patch = 1;
+		revs->merges_imply_patch = 1;
 	} else if (!strcmp(arg, "--cc")) {
 		set_dense_combined(revs);
-		revs->combined_imply_patch = 1;
+		revs->merges_imply_patch = 1;
 	} else if (!strcmp(arg, "--no-diff-merges")) {
 		suppress(revs);
 	} else if (!strcmp(arg, "--combined-all-paths")) {
@@ -155,15 +154,18 @@ void diff_merges_set_dense_combined_if_unset(struct rev_info *revs)
 
 void diff_merges_setup_revs(struct rev_info *revs)
 {
+	if (suppress_parsing)
+		return;
+
 	if (revs->combine_merges == 0)
 		revs->dense_combined_merges = 0;
 	if (revs->separate_merges == 0)
 		revs->first_parent_merges = 0;
 	if (revs->combined_all_paths && !revs->combine_merges)
 		die("--combined-all-paths makes no sense without -c or --cc");
-	if (revs->combined_imply_patch)
+	if (revs->merges_imply_patch)
 		revs->diff = 1;
-	if (revs->combined_imply_patch || revs->merges_need_diff) {
+	if (revs->merges_imply_patch || revs->merges_need_diff) {
 		if (!revs->diffopt.output_format)
 			revs->diffopt.output_format = DIFF_FORMAT_PATCH;
 	}
diff --git a/diff-merges.h b/diff-merges.h
index 09d9a6c9a4f..b5d57f6563e 100644
--- a/diff-merges.h
+++ b/diff-merges.h
@@ -11,6 +11,8 @@ struct rev_info;
 
 int diff_merges_config(const char *value);
 
+void diff_merges_suppress_options_parsing(void);
+
 int diff_merges_parse_opts(struct rev_info *revs, const char **argv);
 
 void diff_merges_suppress(struct rev_info *revs);
diff --git a/perl/Git/SVN.pm b/perl/Git/SVN.pm
index f6f1dc03c60..35ff5a68963 100644
--- a/perl/Git/SVN.pm
+++ b/perl/Git/SVN.pm
@@ -1636,7 +1636,7 @@ sub has_no_changes {
 	my $commit = shift;
 
 	my @revs = split / /, command_oneline(
-		qw(rev-list --parents -1 -m), $commit);
+		qw(rev-list --parents -1), $commit);
 
 	# Commits with no parents, e.g. the start of a partial branch,
 	# have changes by definition.
diff --git a/revision.h b/revision.h
index 93aa012f518..17698cb51ac 100644
--- a/revision.h
+++ b/revision.h
@@ -193,10 +193,10 @@ struct rev_info {
 			/* Diff-merge flags */
 			explicit_diff_merges: 1,
 			merges_need_diff: 1,
+			merges_imply_patch:1,
 			separate_merges: 1,
 			combine_merges:1,
 			combined_all_paths:1,
-			combined_imply_patch:1,
 			dense_combined_merges:1,
 			first_parent_merges:1;
 
diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
index 5f282ecf617..873aa56e359 100755
--- a/t/t3903-stash.sh
+++ b/t/t3903-stash.sh
@@ -859,7 +859,7 @@ test_expect_success 'setup stash with index and worktree changes' '
 	git stash
 '
 
-test_expect_success 'stash list implies --first-parent -m' '
+test_expect_success 'stash list -p shows simple diff' '
 	cat >expect <<-EOF &&
 	stash@{0}
 
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 87def81699b..7fadc985ccc 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -293,6 +293,7 @@ diff-tree --stat initial mode
 diff-tree --summary initial mode
 
 diff-tree master
+diff-tree -m master
 diff-tree -p master
 diff-tree -p -m master
 diff-tree -c master
@@ -337,6 +338,8 @@ log -m -p --first-parent master
 log -m -p master
 log --cc -m -p master
 log -c -m -p master
+log -m --raw master
+log -m --stat master
 log -SF master
 log -S F master
 log -SF -p master
@@ -452,6 +455,14 @@ diff-tree --stat --compact-summary initial mode
 diff-tree -R --stat --compact-summary initial mode
 EOF
 
+test_expect_success 'log -m matches log -m -p' '
+	git log -m -p master >result &&
+	process_diffs result >expected &&
+	git log -m >result &&
+	process_diffs result >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'log --diff-merges=on matches --diff-merges=separate' '
 	git log -p --diff-merges=separate master >result &&
 	process_diffs result >expected &&
@@ -483,6 +494,19 @@ test_expect_success 'git config log.diffMerges first-parent vs -m' '
 	test_cmp expected actual
 '
 
+# -m in "git diff-index" means "match missing", that differs
+# from its meaning in "git diff". Let's check it in diff-index.
+# The line in the output for removed file should disappear when
+# we provide -m in diff-index.
+test_expect_success 'git diff-index -m' '
+	rm -f file1 &&
+	git diff-index HEAD >without-m &&
+	lines_count=$(wc -l <without-m) &&
+	git diff-index -m HEAD >with-m &&
+	git restore file1 &&
+	test_line_count = $((lines_count - 1)) with-m
+'
+
 test_expect_success 'log -S requires an argument' '
 	test_must_fail git log -S
 '
diff --git a/t/t4013/diff.diff-tree_-m_master b/t/t4013/diff.diff-tree_-m_master
new file mode 100644
index 00000000000..6d0a2207fb3
--- /dev/null
+++ b/t/t4013/diff.diff-tree_-m_master
@@ -0,0 +1,11 @@
+$ git diff-tree -m master
+59d314ad6f356dd08601a4cd5e530381da3e3c64
+:040000 040000 65f5c9dd60ce3b2b3324b618ac7accf8d912c113 0564e026437809817a64fff393079714b6dd4628 M	dir
+:100644 100644 b414108e81e5091fe0974a1858b4d0d22b107f70 10a8a9f3657f91a156b9f0184ed79a20adef9f7f M	file0
+59d314ad6f356dd08601a4cd5e530381da3e3c64
+:040000 040000 f977ed46ae6873c1c30ab878e15a4accedc3618b 0564e026437809817a64fff393079714b6dd4628 M	dir
+:100644 100644 f4615da674c09df322d6ba8d6b21ecfb1b1ba510 10a8a9f3657f91a156b9f0184ed79a20adef9f7f M	file0
+:000000 100644 0000000000000000000000000000000000000000 b1e67221afe8461efd244b487afca22d46b95eb8 A	file1
+:100644 000000 01e79c32a8c99c557f0757da7cb6d65b3414466d 0000000000000000000000000000000000000000 D	file2
+:100644 000000 7289e35bff32727c08dda207511bec138fdb9ea5 0000000000000000000000000000000000000000 D	file3
+$
diff --git a/t/t4013/diff.log_-m_--raw_master b/t/t4013/diff.log_-m_--raw_master
new file mode 100644
index 00000000000..cd2ecc46283
--- /dev/null
+++ b/t/t4013/diff.log_-m_--raw_master
@@ -0,0 +1,61 @@
+$ git log -m --raw master
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (from 9a6d4949b6b76956d9d5e26f2791ec2ceff5fdc0)
+Merge: 9a6d494 c7a2ab9
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:04:00 2006 +0000
+
+    Merge branch 'side'
+
+:100644 100644 cead32e... 992913c... M	dir/sub
+:100644 100644 b414108... 10a8a9f... M	file0
+
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (from c7a2ab9e8eac7b117442a607d5a9b3950ae34d5a)
+Merge: 9a6d494 c7a2ab9
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:04:00 2006 +0000
+
+    Merge branch 'side'
+
+:100644 100644 7289e35... 992913c... M	dir/sub
+:100644 100644 f4615da... 10a8a9f... M	file0
+:000000 100644 0000000... b1e6722... A	file1
+:100644 000000 01e79c3... 0000000... D	file2
+:100644 000000 7289e35... 0000000... D	file3
+
+commit c7a2ab9e8eac7b117442a607d5a9b3950ae34d5a
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:03:00 2006 +0000
+
+    Side
+
+:100644 100644 35d242b... 7289e35... M	dir/sub
+:100644 100644 01e79c3... f4615da... M	file0
+:000000 100644 0000000... 7289e35... A	file3
+
+commit 9a6d4949b6b76956d9d5e26f2791ec2ceff5fdc0
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:02:00 2006 +0000
+
+    Third
+
+:100644 100644 8422d40... cead32e... M	dir/sub
+:000000 100644 0000000... b1e6722... A	file1
+
+commit 1bde4ae5f36c8d9abe3a0fce0c6aab3c4a12fe44
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:01:00 2006 +0000
+
+    Second
+    
+    This is the second commit.
+
+:100644 100644 35d242b... 8422d40... M	dir/sub
+:100644 100644 01e79c3... b414108... M	file0
+:100644 000000 01e79c3... 0000000... D	file2
+
+commit 444ac553ac7612cc88969031b02b3767fb8a353a
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:00:00 2006 +0000
+
+    Initial
+$
diff --git a/t/t4013/diff.log_-m_--stat_master b/t/t4013/diff.log_-m_--stat_master
new file mode 100644
index 00000000000..c7db084fd90
--- /dev/null
+++ b/t/t4013/diff.log_-m_--stat_master
@@ -0,0 +1,66 @@
+$ git log -m --stat master
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (from 9a6d4949b6b76956d9d5e26f2791ec2ceff5fdc0)
+Merge: 9a6d494 c7a2ab9
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:04:00 2006 +0000
+
+    Merge branch 'side'
+
+ dir/sub | 2 ++
+ file0   | 3 +++
+ 2 files changed, 5 insertions(+)
+
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (from c7a2ab9e8eac7b117442a607d5a9b3950ae34d5a)
+Merge: 9a6d494 c7a2ab9
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:04:00 2006 +0000
+
+    Merge branch 'side'
+
+ dir/sub | 4 ++++
+ file0   | 3 +++
+ file1   | 3 +++
+ file2   | 3 ---
+ file3   | 4 ----
+ 5 files changed, 10 insertions(+), 7 deletions(-)
+
+commit c7a2ab9e8eac7b117442a607d5a9b3950ae34d5a
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:03:00 2006 +0000
+
+    Side
+
+ dir/sub | 2 ++
+ file0   | 3 +++
+ file3   | 4 ++++
+ 3 files changed, 9 insertions(+)
+
+commit 9a6d4949b6b76956d9d5e26f2791ec2ceff5fdc0
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:02:00 2006 +0000
+
+    Third
+
+ dir/sub | 2 ++
+ file1   | 3 +++
+ 2 files changed, 5 insertions(+)
+
+commit 1bde4ae5f36c8d9abe3a0fce0c6aab3c4a12fe44
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:01:00 2006 +0000
+
+    Second
+    
+    This is the second commit.
+
+ dir/sub | 2 ++
+ file0   | 3 +++
+ file2   | 3 ---
+ 3 files changed, 5 insertions(+), 3 deletions(-)
+
+commit 444ac553ac7612cc88969031b02b3767fb8a353a
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:00:00 2006 +0000
+
+    Initial
+$