diff --git a/usr.bin/xinstall/tests/install_test.sh b/usr.bin/xinstall/tests/install_test.sh
--- a/usr.bin/xinstall/tests/install_test.sh
+++ b/usr.bin/xinstall/tests/install_test.sh
@@ -428,6 +428,8 @@
 	local cu=65532 cg=65532
 	local u="$(id -u)"
 	local g="$(id -g)"
+	local iu="invlid_user"
+	local ig="invlid_group"
 	local m=0755 cm=4444
 	printf "test" >testf
 	atf_check chown "$fu:$fg" testf
@@ -456,6 +458,15 @@
 
 	atf_check install -o "$cu" -g "$cg" -m "$cm" testf testc
 	atf_check_equal "$cu:$cg:10$cm" "$(stat -f"%u:%g:%p" testc)"
+
+	atf_check -o match:"uid=${u} gid=${g}" \
+	    install -M /dev/stdout -o "$u" -g "$g" testf testc
+
+	atf_check -s not-exit:0 -e match:"unknown user ${iu}" \
+	    install -M /dev/stdout -o "$iu" testf testc
+
+	atf_check -s not-exit:0 -e match:"unknown group ${ig}" \
+	    install -M /dev/stdout -g "$ig" testf testc
 }
 
 atf_test_case set_owner_group_mode_unpriv
@@ -467,6 +478,8 @@
 	local cu=65532 cg=65532
 	local u="$(id -u)"
 	local g="$(id -g)"
+	local iu="invalid_user"
+	local ig="invalid_group"
 	local m=0755 cm=4444 cM=0444
 	printf "test" >testf
 	atf_check chown "$fu:$fg" testf
@@ -495,6 +508,48 @@
 
 	atf_check install -U -o "$cu" -g "$cg" -m "$cm" testf testc
 	atf_check_equal "$u:$g:10$cM" "$(stat -f"%u:%g:%p" testc)"
+
+	atf_check -o match:"uid=${u} gid=${g}" \
+	    install -U -M /dev/stdout -o "$u" -g "$g" testf testc
+
+	atf_check -o match:"uname=${iu} gname=${ig}" \
+	    install -U -M /dev/stdout -o "$iu" -g "$ig" testf testc
+}
+
+atf_test_case set_owner_group_mode_numeric_invalid
+set_owner_group_mode_numeric_invalid_head() {
+	atf_set "require.user" "root"
+}
+set_owner_group_mode_numeric_invalid_body() {
+	local UID_MAX=$((1 << 32))
+	local GID_MAX=$((1 << 32))
+	local u="$(id -u)"
+	local g="$(id -g)"
+	printf "test" >testf
+
+	atf_check -s not-exit:0 -e match:"invalid user -1" \
+	    install -o -1 testf testc
+
+	atf_check -s not-exit:0 -e match:"invalid user -1" \
+	    install -U -o -1 testf testc
+
+	atf_check -s not-exit:0 -e match:"invalid group -1" \
+	    install -g -1 testf testc
+
+	atf_check -s not-exit:0 -e match:"invalid group -1" \
+	    install -U -g -1 testf testc
+
+	atf_check -s not-exit:0 -e match:"invalid user ${UID_MAX}" \
+	    install -o "$UID_MAX" testf testc
+
+	atf_check -s not-exit:0 -e match:"invalid user ${UID_MAX}" \
+	    install -U -o "$UID_MAX" testf testc
+
+	atf_check -s not-exit:0 -e match:"invalid group ${GID_MAX}" \
+	    install -g "$GID_MAX" testf testc
+
+	atf_check -s not-exit:0 -e match:"invalid group ${GID_MAX}" \
+	    install -U -g "$GID_MAX" testf testc
 }
 
 atf_test_case set_optional_exec
@@ -556,5 +611,6 @@
 	atf_add_test_case mkdir_simple
 	atf_add_test_case set_owner_group_mode
 	atf_add_test_case set_owner_group_mode_unpriv
+	atf_add_test_case set_owner_group_mode_numeric_invalid
 	atf_add_test_case set_optional_exec
 }
diff --git a/usr.bin/xinstall/xinstall.c b/usr.bin/xinstall/xinstall.c
--- a/usr.bin/xinstall/xinstall.c
+++ b/usr.bin/xinstall/xinstall.c
@@ -324,22 +324,32 @@
 	}
 
 	/* get group and owner id's */
-	if (group != NULL && !dounpriv) {
-		if (gid_from_group(group, &gid) == -1) {
-			id_t id;
+	if (group != NULL) {
+		id_t id;
+
+		if (parseid(group, &id)) {
+			if (id < 0 || id > GID_MAX)
+				errx(1, "invalid group %s", group);
+		}
+		if (!dounpriv && gid_from_group(group, &gid) == -1) {
 			if (!parseid(group, &id))
 				errx(1, "unknown group %s", group);
-			gid = id;
+			gid = (gid_t)id;
 		}
 	} else
 		gid = (gid_t)-1;
 
-	if (owner != NULL && !dounpriv) {
-		if (uid_from_user(owner, &uid) == -1) {
-			id_t id;
+	if (owner != NULL) {
+		id_t id;
+
+		if (parseid(owner, &id)) {
+			if (id < 0 || id > UID_MAX)
+				errx(1, "invalid user %s", owner);
+		}
+		if (!dounpriv && uid_from_user(owner, &uid) == -1) {
 			if (!parseid(owner, &id))
 				errx(1, "unknown user %s", owner);
-			uid = id;
+			uid = (uid_t)id;
 		}
 	} else
 		uid = (uid_t)-1;