diff --git a/libcxx/include/locale b/libcxx/include/locale
--- a/libcxx/include/locale
+++ b/libcxx/include/locale
@@ -1925,7 +1925,7 @@
                                               const ctype<char_type>& __ct) const
 {
     int __t = __get_up_to_n_digits(__b, __e, __err, __ct, 2) - 1;
-    if (!(__err & ios_base::failbit) && __t <= 11)
+    if (!(__err & ios_base::failbit) && 0 <= __t && __t <= 11)
         __m = __t;
     else
         __err |= ios_base::failbit;
diff --git a/libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp b/libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp
--- a/libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp
+++ b/libcxx/test/std/localization/locale.categories/category.time/locale.time.get.byname/get_date.pass.cpp
@@ -104,5 +104,57 @@
         assert(t.tm_year == 109);
         assert(err == std::ios_base::eofbit);
     }
+    // Months must be > 0 and <= 12.
+    {
+        const my_facet f(LOCALE_en_US_UTF_8, 1);
+        const char in[] = "00/21/2022";
+        err = std::ios_base::goodbit;
+        t = std::tm();
+        I i = f.get_date(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
+#if _LIBCPP_VERSION
+          // libc++ points to the '/' after the month.
+          assert(base(i) == in+2);
+#else
+          // libstdc++ points to the second character.
+          assert(base(i) == in+1);
+#endif
+        // tm is not modified.
+        assert(t.tm_mon == 0);
+        assert(t.tm_mday == 0);
+        assert(t.tm_year == 0);
+        assert(err == std::ios_base::failbit);
+    }
+    {
+        const my_facet f(LOCALE_en_US_UTF_8, 1);
+        const char in[] = "13/21/2022";
+        err = std::ios_base::goodbit;
+        t = std::tm();
+        I i = f.get_date(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
+#if _LIBCPP_VERSION
+          // libc++ points to the '/' after the month.
+          assert(base(i) == in+2);
+#else
+          // libstdc++ points to the second character.
+          assert(base(i) == in+1);
+#endif
+        assert(base(i) == in+2);
+        assert(t.tm_mon == 0);
+        assert(t.tm_mday == 0);
+        assert(t.tm_year == 0);
+        assert(err == std::ios_base::failbit);
+    }
+    // Leading zero is allowed.
+    {
+        const my_facet f(LOCALE_en_US_UTF_8, 1);
+        const char in[] = "03/21/2022";
+        err = std::ios_base::goodbit;
+        t = std::tm();
+        I i = f.get_date(I(in), I(in+sizeof(in)/sizeof(in[0])-1), ios, err, &t);
+        assert(base(i) == in+sizeof(in)/sizeof(in[0])-1);
+        assert(t.tm_mon == 2);
+        assert(t.tm_mday == 21);
+        assert(t.tm_year == 122);
+        assert(err == std::ios_base::eofbit);
+    }
   return 0;
 }