diff --git a/lib/libc/db/hash/hash.c b/lib/libc/db/hash/hash.c
--- a/lib/libc/db/hash/hash.c
+++ b/lib/libc/db/hash/hash.c
@@ -99,11 +99,6 @@
 	DB *dbp;
 	int bpages, hdrsize, new_table, nsegs, save_errno;
 
-	if ((flags & O_ACCMODE) == O_WRONLY) {
-		errno = EINVAL;
-		return (NULL);
-	}
-
 	if (!(hashp = (HTAB *)calloc(1, sizeof(HTAB))))
 		return (NULL);
 	hashp->fp = -1;
@@ -115,6 +110,10 @@
 	 * we can check accesses.
 	 */
 	hashp->flags = flags;
+	if ((flags & O_ACCMODE) == O_WRONLY) {
+		flags &= ~O_WRONLY;
+		flags |= O_RDWR;
+	}
 
 	if (file) {
 		if ((hashp->fp = _open(file, flags | O_CLOEXEC, mode)) == -1)
diff --git a/lib/libc/db/man/dbm.3 b/lib/libc/db/man/dbm.3
--- a/lib/libc/db/man/dbm.3
+++ b/lib/libc/db/man/dbm.3
@@ -13,7 +13,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd April 2, 2022
+.Dd July 25, 2025
 .Dt DBM 3
 .Os
 .Sh NAME
@@ -99,9 +99,6 @@
 .Li 0660
 is a typical value for
 .Fa mode .
-.Dv O_WRONLY
-is not allowed in
-.Fa flags .
 The pointer returned by
 .Fn dbm_open
 identifies the database and is the
diff --git a/lib/libc/tests/db/dbm_open_test.c b/lib/libc/tests/db/dbm_open_test.c
--- a/lib/libc/tests/db/dbm_open_test.c
+++ b/lib/libc/tests/db/dbm_open_test.c
@@ -12,6 +12,9 @@
 
 #include <atf-c.h>
 
+static const char *path = "tmp";
+static const char *dbname = "tmp.db";
+
 ATF_TC(dbm_open_missing_test);
 ATF_TC_HEAD(dbm_open_missing_test, tc)
 {
@@ -21,8 +24,6 @@
 
 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
@@ -36,8 +37,18 @@
 	ATF_CHECK(dbm_open(path, O_RDONLY | O_CREAT | O_EXCL, _PROT_ALL) == NULL);
 }
 
+ATF_TC_WITHOUT_HEAD(dbm_open_wronly_test);
+ATF_TC_BODY(dbm_open_wronly_test, tc)
+{
+        ATF_CHECK(dbm_open(path, O_WRONLY, _PROT_ALL) == NULL);
+        ATF_REQUIRE(!atf_utils_file_exists(dbname));
+        ATF_CHECK(dbm_open(path, O_WRONLY | O_CREAT, _PROT_ALL) != NULL);
+        ATF_REQUIRE(atf_utils_file_exists(dbname));
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 	ATF_TP_ADD_TC(tp, dbm_open_missing_test);
+	ATF_TP_ADD_TC(tp, dbm_open_wronly_test);
 	return (atf_no_error());
 }