diff --git a/diff.c b/diff.c
index d2139082b767433e17b7a070b615c6870869b51e..2c904e0526d52437677b6d965b02d400c94c8062 100644
--- a/diff.c
+++ b/diff.c
@@ -4909,6 +4909,22 @@ static int diff_opt_dirstat(const struct option *opt,
 	return 0;
 }
 
+static int diff_opt_find_renames(const struct option *opt,
+				 const char *arg, int unset)
+{
+	struct diff_options *options = opt->value;
+
+	BUG_ON_OPT_NEG(unset);
+	if (!arg)
+		arg = "";
+	options->rename_score = parse_rename_score(&arg);
+	if (*arg != 0)
+		return error(_("invalid argument to %s"), opt->long_name);
+
+	options->detect_rename = DIFF_DETECT_RENAME;
+	return 0;
+}
+
 static enum parse_opt_result diff_opt_output(struct parse_opt_ctx_t *ctx,
 					     const struct option *opt,
 					     const char *arg, int unset)
@@ -5040,6 +5056,10 @@ static void prep_parse_options(struct diff_options *options)
 			       N_("break complete rewrite changes into pairs of delete and create"),
 			       PARSE_OPT_NONEG | PARSE_OPT_OPTARG,
 			       diff_opt_break_rewrites),
+		OPT_CALLBACK_F('M', "find-renames", options, N_("<n>"),
+			       N_("detect renames"),
+			       PARSE_OPT_NONEG | PARSE_OPT_OPTARG,
+			       diff_opt_find_renames),
 
 		OPT_GROUP(N_("Diff other options")),
 		{ OPTION_CALLBACK, 0, "output", options, N_("<file>"),
@@ -5074,13 +5094,7 @@ int diff_opt_parse(struct diff_options *options,
 		return ac;
 
 	/* renames options */
-	if (starts_with(arg, "-M") ||
-		 skip_to_optional_arg(arg, "--find-renames", NULL)) {
-		if ((options->rename_score = diff_scoreopt_parse(arg)) == -1)
-			return error("invalid argument to -M: %s", arg+2);
-		options->detect_rename = DIFF_DETECT_RENAME;
-	}
-	else if (!strcmp(arg, "-D") || !strcmp(arg, "--irreversible-delete")) {
+	if (!strcmp(arg, "-D") || !strcmp(arg, "--irreversible-delete")) {
 		options->irreversible_delete = 1;
 	}
 	else if (starts_with(arg, "-C") ||
@@ -5363,13 +5377,10 @@ static int diff_scoreopt_parse(const char *opt)
 		if (skip_prefix(opt, "find-copies", &opt)) {
 			if (*opt == 0 || *opt++ == '=')
 				cmd = 'C';
-		} else if (skip_prefix(opt, "find-renames", &opt)) {
-			if (*opt == 0 || *opt++ == '=')
-				cmd = 'M';
 		}
 	}
-	if (cmd != 'M' && cmd != 'C')
-		return -1; /* that is not a -M, or -C option */
+	if (cmd != 'C')
+		return -1; /* that is not a -M option */
 
 	opt1 = parse_rename_score(&opt);
 	if (*opt != 0)