diff --git a/src/LdifDotNet/RfcGrammar.cs b/src/LdifDotNet/RfcGrammar.cs
index 3a615f8..204f435 100644
--- a/src/LdifDotNet/RfcGrammar.cs
+++ b/src/LdifDotNet/RfcGrammar.cs
@@ -15,7 +15,15 @@ internal static class RfcGrammar
     /// </summary>
     internal static readonly UTF8Encoding StrictUtf8 = new(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true);
 
-    /// <summary>RFC 4512 numericoid / RFC 2849 ldap-oid: 1*DIGIT *("." 1*DIGIT).</summary>
+    /// <summary>
+    /// Numeric OID, deliberately the looser RFC 2849 ldap-oid grammar
+    /// (1*DIGIT *("." 1*DIGIT)) rather than RFC 4512's numericoid: leading-zero
+    /// arcs and single-arc OIDs are accepted. Correct per spec on every LDIF
+    /// boundary, and matched to slapd on the schema boundary — slaptest 2.6
+    /// accepts 01.2.3.4.5, 1.02.3, and bare 1 in attributetype directives, so
+    /// tightening this would reject files slapd loads. Pinned by tests; do not
+    /// "fix" toward RFC 4512 without re-probing slapd.
+    /// </summary>
     internal static bool IsNumericOid(string text)
     {
         bool expectDigit = true;
diff --git a/tests/LdifDotNet.Tests/AttributeDescriptionTests.cs b/tests/LdifDotNet.Tests/AttributeDescriptionTests.cs
index b4c8309..748dca6 100644
--- a/tests/LdifDotNet.Tests/AttributeDescriptionTests.cs
+++ b/tests/LdifDotNet.Tests/AttributeDescriptionTests.cs
@@ -26,6 +26,7 @@ public void HasOption_matches_whole_options_case_insensitively(string descriptio
     [Theory]
     [InlineData("cn", true)]
     [InlineData("2.5.4.3", true)]
+    [InlineData("01.2.3", true)] // RFC 2849 ldap-oid allows leading zeros — deliberate, see RfcGrammar.IsNumericOid
     [InlineData("userCertificate;binary", true)]
     [InlineData("cn;lang-en;binary", true)]
     [InlineData("", false)]
diff --git a/tests/LdifDotNet.Tests/SchemaParserTests.cs b/tests/LdifDotNet.Tests/SchemaParserTests.cs
index 6cde7cc..4e0e63b 100644
--- a/tests/LdifDotNet.Tests/SchemaParserTests.cs
+++ b/tests/LdifDotNet.Tests/SchemaParserTests.cs
@@ -12,6 +12,23 @@ public static TheoryData<string> SchemaFiles()
         return data;
     }
 
+    [Theory]
+    [InlineData("01.2.3.4.5")] // leading-zero arc — illegal per RFC 4512 numericoid
+    [InlineData("1.02.3")]     // interior leading zero
+    [InlineData("1")]          // single arc — RFC 4512 requires at least two
+    public void Oid_leniency_matches_slapd_not_rfc4512(string oid)
+    {
+        // Deliberate: IsNumericOid implements RFC 2849's looser ldap-oid, and
+        // slapd is exactly as loose — slaptest (OpenLDAP 2.6.10, 2026-08-03)
+        // accepted attributetype directives with every OID shape below.
+        // Tightening to RFC 4512's numericoid would reject schema files slapd
+        // loads, breaking the tolerant-reader / slapd-compatibility invariant.
+        var schema = LdapSchema.Parse(
+            $"attributetype ( {oid} NAME 'probeAttr' SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )\n");
+
+        Assert.Equal(oid, schema.AttributeTypes[0].Oid);
+    }
+
     [Fact]
     public void Ldapsyntax_directive_parses_in_file_mode()
     {