diff --git a/diff.c b/diff.c
index db5e84443b..6991ed4e17 100644
--- a/diff.c
+++ b/diff.c
@@ -3152,12 +3152,12 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 	else if (!prefixcmp(arg, "-B") || !prefixcmp(arg, "--break-rewrites=") ||
 		 !strcmp(arg, "--break-rewrites")) {
 		if ((options->break_opt = diff_scoreopt_parse(arg)) == -1)
-			return -1;
+			return error("invalid argument to -B: %s", arg+2);
 	}
 	else if (!prefixcmp(arg, "-M") || !prefixcmp(arg, "--detect-renames=") ||
 		 !strcmp(arg, "--detect-renames")) {
 		if ((options->rename_score = diff_scoreopt_parse(arg)) == -1)
-			return -1;
+			return error("invalid argument to -M: %s", arg+2);
 		options->detect_rename = DIFF_DETECT_RENAME;
 	}
 	else if (!prefixcmp(arg, "-C") || !prefixcmp(arg, "--detect-copies=") ||
@@ -3165,7 +3165,7 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		if (options->detect_rename == DIFF_DETECT_COPY)
 			DIFF_OPT_SET(options, FIND_COPIES_HARDER);
 		if ((options->rename_score = diff_scoreopt_parse(arg)) == -1)
-			return -1;
+			return error("invalid argument to -C: %s", arg+2);
 		options->detect_rename = DIFF_DETECT_COPY;
 	}
 	else if (!strcmp(arg, "--no-renames"))