diff --git a/lib/prototypes.h b/lib/prototypes.h
index 3a04faa8..722d6d98 100644
--- a/lib/prototypes.h
+++ b/lib/prototypes.h
@@ -358,6 +358,7 @@ extern void pw_free (/*@out@*/ /*@only@*/struct passwd *pwent);
 
 /* csrand.c */
 unsigned long csrand (void);
+unsigned long csrand_uniform (unsigned long n);
 
 /* remove_tree.c */
 extern int remove_tree (const char *root, bool remove_root);
diff --git a/libmisc/csrand.c b/libmisc/csrand.c
index a0237850..0cc99972 100644
--- a/libmisc/csrand.c
+++ b/libmisc/csrand.c
@@ -1,3 +1,9 @@
+/*
+ * SPDX-FileCopyrightText:  Alejandro Colomar <alx@kernel.org>
+ *
+ * SPDX-License-Identifier:  BSD-3-Clause
+ */
+
 #include <config.h>
 
 #ident "$Id$"
@@ -59,3 +65,23 @@ fail:
 	fprintf(log_get_logfd(), _("Unable to obtain random bytes.\n"));
 	exit(1);
 }
+
+
+/*
+ * Return a uniformly-distributed CS random value in the interval [0, n-1].
+ */
+unsigned long
+csrand_uniform(unsigned long n)
+{
+	unsigned long  r, max, mask;
+
+	max = n - 1;
+	mask = bit_ceil_wrapul(n) - 1;
+
+	do {
+		r = csrand();
+		r &= mask;  // optimization
+	} while (r > max);  // p = ((mask + 1) % n) / (mask + 1); W.C.: p=0.5
+
+	return r;
+}