diff --git a/src/lib.rs b/src/lib.rs
index 7742e1c6..ceaad18d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -911,7 +911,7 @@ impl CertificateParams {
 			// Write extensions
 			// According to the spec in RFC 2986, even if attributes are empty we need the empty attribute tag
 			writer.next().write_tagged(Tag::context(0), |writer| {
-				if !subject_alt_names.is_empty() {
+				if !subject_alt_names.is_empty() || !custom_extensions.is_empty() {
 					writer.write_sequence(|writer| {
 						let oid = ObjectIdentifier::from_slice(OID_PKCS_9_AT_EXTENSION_REQUEST);
 						writer.next().write_oid(&oid);
@@ -922,17 +922,12 @@ impl CertificateParams {
 
 								// Write custom extensions
 								for ext in custom_extensions {
-									writer.next().write_sequence(|writer| {
-										let oid = ObjectIdentifier::from_slice(&ext.oid);
-										writer.next().write_oid(&oid);
-										// If the extension is critical, we should signal this.
-										// It's false by default so we don't need to write anything
-										// if the extension is not critical.
-										if ext.critical {
-											writer.next().write_bool(true);
-										}
-										writer.next().write_bytes(&ext.content);
-									});
+									write_x509_extension(
+										writer.next(),
+										&ext.oid,
+										ext.critical,
+										|writer| writer.write_der(ext.content()),
+									);
 								}
 							});
 						});
@@ -999,11 +994,7 @@ impl CertificateParams {
 
 						// Write standard key usage
 						if !self.key_usages.is_empty() {
-							writer.next().write_sequence(|writer| {
-								let oid = ObjectIdentifier::from_slice(OID_KEY_USAGE);
-								writer.next().write_oid(&oid);
-								writer.next().write_bool(true);
-
+							write_x509_extension(writer.next(), OID_KEY_USAGE, true, |writer| {
 								let mut bits: u16 = 0;
 
 								for entry in self.key_usages.iter() {
@@ -1032,12 +1023,7 @@ impl CertificateParams {
 								// Finally take only the bytes != 0
 								let bits = &bits[..nb];
 
-								let der = yasna::construct_der(|writer| {
-									writer.write_bitvec_bytes(&bits, msb as usize)
-								});
-
-								// Write them
-								writer.next().write_bytes(&der);
+								writer.write_bitvec_bytes(&bits, msb as usize)
 							});
 						}
 
@@ -1157,16 +1143,8 @@ impl CertificateParams {
 
 						// Write the custom extensions
 						for ext in &self.custom_extensions {
-							writer.next().write_sequence(|writer| {
-								let oid = ObjectIdentifier::from_slice(&ext.oid);
-								writer.next().write_oid(&oid);
-								// If the extension is critical, we should signal this.
-								// It's false by default so we don't need to write anything
-								// if the extension is not critical.
-								if ext.critical {
-									writer.next().write_bool(true);
-								}
-								writer.next().write_bytes(&ext.content);
+							write_x509_extension(writer.next(), &ext.oid, ext.critical, |writer| {
+								writer.write_der(ext.content())
 							});
 						}
 					});
diff --git a/tests/generic.rs b/tests/generic.rs
index 647eb7df..2b158c7c 100644
--- a/tests/generic.rs
+++ b/tests/generic.rs
@@ -84,6 +84,77 @@ mod test_convert_x509_subject_alternative_name {
 	}
 }
 
+#[cfg(feature = "x509-parser")]
+mod test_x509_custom_ext {
+	use crate::util;
+	use crate::Certificate;
+
+	use rcgen::CustomExtension;
+	use x509_parser::oid_registry::asn1_rs;
+	use x509_parser::prelude::{
+		FromDer, ParsedCriAttribute, X509Certificate, X509CertificationRequest,
+	};
+
+	#[test]
+	fn custom_ext() {
+		// Create an imaginary critical custom extension for testing.
+		let test_oid = asn1_rs::Oid::from(&[2, 5, 29, 999999]).unwrap();
+		let test_ext = yasna::construct_der(|writer| {
+			writer.write_utf8_string("🦀 greetz to ferris 🦀");
+		});
+		let mut custom_ext = CustomExtension::from_oid_content(
+			test_oid.iter().unwrap().collect::<Vec<u64>>().as_slice(),
+			test_ext.clone(),
+		);
+		custom_ext.set_criticality(true);
+
+		// Generate a certificate with the custom extension, parse it with x509-parser.
+		let mut params = util::default_params();
+		params.custom_extensions = vec![custom_ext];
+		// Ensure the custom exts. being omitted into a CSR doesn't require SAN ext being present.
+		// See https://github.com/rustls/rcgen/issues/122
+		params.subject_alt_names = Vec::default();
+		let test_cert = Certificate::from_params(params).unwrap();
+		let test_cert_der = test_cert.serialize_der().unwrap();
+		let (_, x509_test_cert) = X509Certificate::from_der(&test_cert_der).unwrap();
+
+		// We should be able to find the extension by OID, with expected criticality and value.
+		let favorite_drink_ext = x509_test_cert
+			.get_extension_unique(&test_oid)
+			.expect("invalid extensions")
+			.expect("missing custom extension");
+		assert_eq!(favorite_drink_ext.critical, true);
+		assert_eq!(favorite_drink_ext.value, test_ext);
+
+		// Generate a CSR with the custom extension, parse it with x509-parser.
+		let test_cert_csr_der = test_cert.serialize_request_der().unwrap();
+		let (_, x509_csr) = X509CertificationRequest::from_der(&test_cert_csr_der).unwrap();
+
+		// We should find that the CSR contains requested extensions.
+		// Note: we can't use `x509_csr.requested_extensions()` here because it maps the raw extension
+		// request extensions to their parsed form, and of course x509-parser doesn't parse our custom extension.
+		let exts = x509_csr
+			.certification_request_info
+			.iter_attributes()
+			.find_map(|attr| {
+				if let ParsedCriAttribute::ExtensionRequest(requested) = &attr.parsed_attribute() {
+					Some(requested.extensions.iter().collect::<Vec<_>>())
+				} else {
+					None
+				}
+			})
+			.expect("missing requested extensions");
+
+		// We should find the custom extension with expected criticality and value.
+		let custom_ext = exts
+			.iter()
+			.find(|ext| ext.oid == test_oid)
+			.expect("missing requested custom extension");
+		assert_eq!(custom_ext.critical, true);
+		assert_eq!(custom_ext.value, test_ext);
+	}
+}
+
 #[cfg(feature = "x509-parser")]
 mod test_x509_parser_crl {
 	use crate::util;