diff --git a/lib/libc/tests/gen/arc4random_test.c b/lib/libc/tests/gen/arc4random_test.c
index e96ebdc6c6ca..79139f29f8fa 100644
--- a/lib/libc/tests/gen/arc4random_test.c
+++ b/lib/libc/tests/gen/arc4random_test.c
@@ -1,86 +1,112 @@
 /*-
  * Copyright (c) 2011 David Schultz
+ * Copyright (c) 2024 Robert Clausecker <fuz@FreeBSD.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #include <sys/types.h>
 #include <sys/mman.h>
 #include <sys/wait.h>
 #include <errno.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
 #include <atf-c.h>
 
 /*
  * BUFSIZE is the number of bytes of rc4 output to compare.  The probability
  * that this test fails spuriously is 2**(-BUFSIZE * 8).
  */
 #define	BUFSIZE		8
 
 /*
  * Test whether arc4random_buf() returns the same sequence of bytes in both
  * parent and child processes.  (Hint: It shouldn't.)
  */
 ATF_TC_WITHOUT_HEAD(test_arc4random);
 ATF_TC_BODY(test_arc4random, tc)
 {
 	struct shared_page {
 		char parentbuf[BUFSIZE];
 		char childbuf[BUFSIZE];
 	} *page;
 	pid_t pid;
 	char c;
 
 	page = mmap(NULL, sizeof(struct shared_page), PROT_READ | PROT_WRITE,
 		    MAP_ANON | MAP_SHARED, -1, 0);
 	ATF_REQUIRE_MSG(page != MAP_FAILED, "mmap failed; errno=%d", errno);
 
 	arc4random_buf(&c, 1);
 
 	pid = fork();
 	ATF_REQUIRE(0 <= pid);
 	if (pid == 0) {
 		/* child */
 		arc4random_buf(page->childbuf, BUFSIZE);
 		exit(0);
 	} else {
 		/* parent */
 		int status;
 		arc4random_buf(page->parentbuf, BUFSIZE);
 		wait(&status);
 	}
 	ATF_CHECK_MSG(memcmp(page->parentbuf, page->childbuf, BUFSIZE) != 0,
 	    "sequences are the same");
 }
 
+/*
+ * Test whether arc4random_uniform() returns a number below the given threshold.
+ * Test with various thresholds.
+ */
+ATF_TC_WITHOUT_HEAD(test_arc4random_uniform);
+ATF_TC_BODY(test_arc4random_uniform, tc)
+{
+	size_t i, j;
+	static const uint32_t thresholds[] = {
+		1, 2, 3, 4, 5, 10, 100, 1000,
+		INT32_MAX, (uint32_t)INT32_MAX + 1,
+		UINT32_MAX - 1000000000, UINT32_MAX - 1000000, UINT32_MAX - 1, 0
+	};
+
+	for (i = 0; thresholds[i] != 0; i++)
+		for (j = 0; j < 10000; j++)
+			ATF_CHECK(arc4random_uniform(thresholds[i]) < thresholds[i]);
+
+	/* for a threshold of zero, just check that we get zero every time */
+	for (j = 0; j < 1000; j++)
+		ATF_CHECK_EQ(0, arc4random_uniform(0));
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 
 	ATF_TP_ADD_TC(tp, test_arc4random);
+	ATF_TP_ADD_TC(tp, test_arc4random_uniform);
 
 	return (atf_no_error());
 }