Simple software acting as an stdio filter, no third party libraries,
not big churn, so this is a good candidate for pledge.

Index: src/main.c
--- src/main.c.orig
+++ src/main.c
@@ -15,6 +15,7 @@
 
 char *strstr(const char *haystack, const char *needle);
 char *strerror(int errnum);
+int pledge(const char *, const char *);
 
 static struct str *parse_section(struct parser *p) {
 	struct str *section = str_create();
@@ -770,6 +771,12 @@ int main(int argc, char **argv) {
 		fprintf(stderr, "Usage: scdoc < input.scd > output.roff\n");
 		return 1;
 	}
+
+	if (pledge("stdio", NULL) == -1) {
+		fprintf(stderr, "pledge: %s", strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
 	struct parser p = {
 		.input = stdin,
 		.output = stdout,