diff --git a/crypto/bytestring/bytestring_test.cc b/crypto/bytestring/bytestring_test.cc
index e1d16f49..31ee51c4 100644
--- a/crypto/bytestring/bytestring_test.cc
+++ b/crypto/bytestring/bytestring_test.cc
@@ -269,7 +269,7 @@ static bool TestGetOptionalASN1Bool() {
 }
 
 static bool TestCBBBasic() {
-  static const uint8_t kExpected[] = {1, 2, 3, 4, 5, 6, 7, 8};
+  static const uint8_t kExpected[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0xa, 0xb, 0xc};
   uint8_t *buf;
   size_t buf_len;
   CBB cbb;
@@ -285,7 +285,8 @@ static bool TestCBBBasic() {
   if (!CBB_add_u8(&cbb, 1) ||
       !CBB_add_u16(&cbb, 0x203) ||
       !CBB_add_u24(&cbb, 0x40506) ||
-      !CBB_add_bytes(&cbb, (const uint8_t*) "\x07\x08", 2) ||
+      !CBB_add_u32(&cbb, 0x708090a) ||
+      !CBB_add_bytes(&cbb, (const uint8_t*) "\x0b\x0c", 2) ||
       !CBB_finish(&cbb, &buf, &buf_len)) {
     CBB_cleanup(&cbb);
     return false;
diff --git a/crypto/bytestring/cbb.c b/crypto/bytestring/cbb.c
index 8fc51879..6cb7988c 100644
--- a/crypto/bytestring/cbb.c
+++ b/crypto/bytestring/cbb.c
@@ -397,6 +397,14 @@ int CBB_add_u24(CBB *cbb, uint32_t value) {
   return cbb_buffer_add_u(cbb->base, value, 3);
 }
 
+int CBB_add_u32(CBB *cbb, uint32_t value) {
+  if (!CBB_flush(cbb)) {
+    return 0;
+  }
+
+  return cbb_buffer_add_u(cbb->base, value, 4);
+}
+
 void CBB_discard_child(CBB *cbb) {
   if (cbb->child == NULL) {
     return;
diff --git a/include/openssl/bytestring.h b/include/openssl/bytestring.h
index 3a8d4e53..c24281a5 100644
--- a/include/openssl/bytestring.h
+++ b/include/openssl/bytestring.h
@@ -377,6 +377,10 @@ OPENSSL_EXPORT int CBB_add_u16(CBB *cbb, uint16_t value);
  * returns one on success and zero otherwise. */
 OPENSSL_EXPORT int CBB_add_u24(CBB *cbb, uint32_t value);
 
+/* CBB_add_u32 appends a 32-bit, big-endian number from |value| to |cbb|. It
+ * returns one on success and zero otherwise. */
+OPENSSL_EXPORT int CBB_add_u32(CBB *cbb, uint32_t value);
+
 /* CBB_discard_child discards the current unflushed child of |cbb|. Neither the
  * child's contents nor the length prefix will be included in the output. */
 OPENSSL_EXPORT void CBB_discard_child(CBB *cbb);