diff --git a/lib/libc/tests/db/Makefile b/lib/libc/tests/db/Makefile
index f1f33bd2bafc..54b38b94a581 100644
--- a/lib/libc/tests/db/Makefile
+++ b/lib/libc/tests/db/Makefile
@@ -1,18 +1,20 @@
 PACKAGE=	tests
 
 BINDIR=		${TESTSDIR}
 
 PROGS=		h_db
 PROGS+=		h_lfsr
 
 ${PACKAGE}FILES+=		README
 
+ATF_TESTS_C+=		dbm_open_test
+
 NETBSD_ATF_TESTS_C+=	db_hash_seq_test
 NETBSD_ATF_TESTS_SH+=	db_test
 ATF_TESTS_SH_SED_db_test=	-e 's,/bin/csh,/bin/cat,g'
 
 CFLAGS+=	-I${SRCTOP}/lib/libc/db/btree
 
 .include "../Makefile.netbsd-tests"
 
 .include <bsd.test.mk>
diff --git a/lib/libc/tests/db/dbm_open_test.c b/lib/libc/tests/db/dbm_open_test.c
new file mode 100644
index 000000000000..18d398e16b2a
--- /dev/null
+++ b/lib/libc/tests/db/dbm_open_test.c
@@ -0,0 +1,43 @@
+/*-
+ * Copyright (c) 2025 Klara, Inc.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <sys/mman.h>
+
+#include <fcntl.h>
+#include <ndbm.h>
+#include <stdio.h>
+
+#include <atf-c.h>
+
+ATF_TC(dbm_open_missing_test);
+ATF_TC_HEAD(dbm_open_missing_test, tc)
+{
+	atf_tc_set_md_var(tc, "descr",
+	    "Test dbm_open when creating a new database");
+}
+
+ATF_TC_BODY(dbm_open_missing_test, tc)
+{
+	const char *path = "tmp";
+	const char *dbname = "tmp.db";
+
+	/*
+	 * POSIX.1 specifies that a missing database file should
+	 * always get created if O_CREAT is present, except when
+	 * O_EXCL is specified as well.
+	 */
+	ATF_CHECK(dbm_open(path, O_RDONLY, _PROT_ALL) == NULL);
+	ATF_REQUIRE(!atf_utils_file_exists(dbname));
+	ATF_CHECK(dbm_open(path, O_RDONLY | O_CREAT, _PROT_ALL) != NULL);
+	ATF_REQUIRE(atf_utils_file_exists(dbname));
+	ATF_CHECK(dbm_open(path, O_RDONLY | O_CREAT | O_EXCL, _PROT_ALL) == NULL);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, dbm_open_missing_test);
+	return (atf_no_error());
+}