diff --git a/crypto/err/ssl.errordata b/crypto/err/ssl.errordata
index da85b1f..04c7d53 100644
--- a/crypto/err/ssl.errordata
+++ b/crypto/err/ssl.errordata
@@ -79,6 +79,7 @@
 SSL,157,INAPPROPRIATE_FALLBACK
 SSL,303,INCONSISTENT_CLIENT_HELLO
 SSL,259,INVALID_ALPN_PROTOCOL
+SSL,315,INVALID_ALPN_PROTOCOL_LIST
 SSL,314,INVALID_CLIENT_HELLO_INNER
 SSL,158,INVALID_COMMAND
 SSL,256,INVALID_COMPRESSION_LIST
diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index 16b64c1..8d8e091 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -2723,8 +2723,9 @@
 
 // SSL_CTX_set_alpn_protos sets the client ALPN protocol list on |ctx| to
 // |protos|. |protos| must be in wire-format (i.e. a series of non-empty, 8-bit
-// length-prefixed strings). It returns zero on success and one on failure.
-// Configuring this list enables ALPN on a client.
+// length-prefixed strings), or the empty string to disable ALPN. It returns
+// zero on success and one on failure. Configuring a non-empty string enables
+// ALPN on a client.
 //
 // WARNING: this function is dangerous because it breaks the usual return value
 // convention.
@@ -2733,8 +2734,9 @@
 
 // SSL_set_alpn_protos sets the client ALPN protocol list on |ssl| to |protos|.
 // |protos| must be in wire-format (i.e. a series of non-empty, 8-bit
-// length-prefixed strings). It returns zero on success and one on failure.
-// Configuring this list enables ALPN on a client.
+// length-prefixed strings), or the empty string to disable ALPN. It returns
+// zero on success and one on failure. Configuring a non-empty string enables
+// ALPN on a client.
 //
 // WARNING: this function is dangerous because it breaks the usual return value
 // convention.
@@ -5368,6 +5370,7 @@
 #define SSL_R_UNSUPPORTED_ECH_SERVER_CONFIG 312
 #define SSL_R_ECH_SERVER_WOULD_HAVE_NO_RETRY_CONFIGS 313
 #define SSL_R_INVALID_CLIENT_HELLO_INNER 314
+#define SSL_R_INVALID_ALPN_PROTOCOL_LIST 315
 #define SSL_R_SSLV3_ALERT_CLOSE_NOTIFY 1000
 #define SSL_R_SSLV3_ALERT_UNEXPECTED_MESSAGE 1010
 #define SSL_R_SSLV3_ALERT_BAD_RECORD_MAC 1020
diff --git a/ssl/internal.h b/ssl/internal.h
index 7a3979b..e1585c3 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -2052,6 +2052,9 @@
     SSL_HANDSHAKE *hs, Array<uint8_t> *out,
     enum ssl_cert_verify_context_t cert_verify_context);
 
+// ssl_is_valid_alpn_list returns whether |in| is a valid ALPN protocol list.
+bool ssl_is_valid_alpn_list(Span<const uint8_t> in);
+
 // ssl_is_alpn_protocol_allowed returns whether |protocol| is a valid server
 // selection for |hs->ssl|'s client preferences.
 bool ssl_is_alpn_protocol_allowed(const SSL_HANDSHAKE *hs,
diff --git a/ssl/ssl_lib.cc b/ssl/ssl_lib.cc
index 4e820f0..522c09e 100644
--- a/ssl/ssl_lib.cc
+++ b/ssl/ssl_lib.cc
@@ -2300,21 +2300,26 @@
 
 int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const uint8_t *protos,
                             unsigned protos_len) {
-  // Note this function's calling convention is backwards.
-  return ctx->alpn_client_proto_list.CopyFrom(MakeConstSpan(protos, protos_len))
-             ? 0
-             : 1;
+  // Note this function's return value is backwards.
+  auto span = MakeConstSpan(protos, protos_len);
+  if (!span.empty() && !ssl_is_valid_alpn_list(span)) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_ALPN_PROTOCOL_LIST);
+    return 1;
+  }
+  return ctx->alpn_client_proto_list.CopyFrom(span) ? 0 : 1;
 }
 
 int SSL_set_alpn_protos(SSL *ssl, const uint8_t *protos, unsigned protos_len) {
-  // Note this function's calling convention is backwards.
+  // Note this function's return value is backwards.
   if (!ssl->config) {
     return 1;
   }
-  return ssl->config->alpn_client_proto_list.CopyFrom(
-             MakeConstSpan(protos, protos_len))
-             ? 0
-             : 1;
+  auto span = MakeConstSpan(protos, protos_len);
+  if (!span.empty() && !ssl_is_valid_alpn_list(span)) {
+    OPENSSL_PUT_ERROR(SSL, SSL_R_INVALID_ALPN_PROTOCOL_LIST);
+    return 1;
+  }
+  return ssl->config->alpn_client_proto_list.CopyFrom(span) ? 0 : 1;
 }
 
 void SSL_CTX_set_alpn_select_cb(SSL_CTX *ctx,
diff --git a/ssl/ssl_test.cc b/ssl/ssl_test.cc
index 0c6bf50..1f402db 100644
--- a/ssl/ssl_test.cc
+++ b/ssl/ssl_test.cc
@@ -6914,5 +6914,53 @@
   }
 }
 
+TEST(SSLTest, ALPNConfig) {
+  bssl::UniquePtr<SSL_CTX> ctx(SSL_CTX_new(TLS_method()));
+  ASSERT_TRUE(ctx);
+  bssl::UniquePtr<X509> cert = GetTestCertificate();
+  bssl::UniquePtr<EVP_PKEY> key = GetTestKey();
+  ASSERT_TRUE(cert);
+  ASSERT_TRUE(key);
+  ASSERT_TRUE(SSL_CTX_use_certificate(ctx.get(), cert.get()));
+  ASSERT_TRUE(SSL_CTX_use_PrivateKey(ctx.get(), key.get()));
+
+  // Set up some machinery to check the configured ALPN against what is actually
+  // sent over the wire. Note that the ALPN callback is only called when the
+  // client offers ALPN.
+  std::vector<uint8_t> observed_alpn;
+  SSL_CTX_set_alpn_select_cb(
+      ctx.get(),
+      [](SSL *ssl, const uint8_t **out, uint8_t *out_len, const uint8_t *in,
+         unsigned in_len, void *arg) -> int {
+        std::vector<uint8_t> *observed_alpn_ptr =
+            static_cast<std::vector<uint8_t> *>(arg);
+        observed_alpn_ptr->assign(in, in + in_len);
+        return SSL_TLSEXT_ERR_NOACK;
+      },
+      &observed_alpn);
+  auto check_alpn_proto = [&](Span<const uint8_t> expected) {
+    observed_alpn.clear();
+    bssl::UniquePtr<SSL> client, server;
+    EXPECT_TRUE(ConnectClientAndServer(&client, &server, ctx.get(), ctx.get()));
+    EXPECT_EQ(Bytes(expected), Bytes(observed_alpn));
+  };
+
+  // Note that |SSL_CTX_set_alpn_protos|'s return value is reversed.
+  static const uint8_t kValidList[] = {0x03, 'f', 'o', 'o',
+                                       0x03, 'b', 'a', 'r'};
+  EXPECT_EQ(0,
+            SSL_CTX_set_alpn_protos(ctx.get(), kValidList, sizeof(kValidList)));
+  check_alpn_proto(kValidList);
+
+  // Invalid lists are rejected.
+  static const uint8_t kInvalidList[] = {0x04, 'f', 'o', 'o'};
+  EXPECT_EQ(1, SSL_CTX_set_alpn_protos(ctx.get(), kInvalidList,
+                                       sizeof(kInvalidList)));
+
+  // Empty lists are valid and are interpreted as disabling ALPN.
+  EXPECT_EQ(0, SSL_CTX_set_alpn_protos(ctx.get(), nullptr, 0));
+  check_alpn_proto({});
+}
+
 }  // namespace
 BSSL_NAMESPACE_END
diff --git a/ssl/t1_lib.cc b/ssl/t1_lib.cc
index 20517c4..3a88cd1 100644
--- a/ssl/t1_lib.cc
+++ b/ssl/t1_lib.cc
@@ -1528,6 +1528,22 @@
   return true;
 }
 
+bool ssl_is_valid_alpn_list(Span<const uint8_t> in) {
+  CBS protocol_name_list = in;
+  if (CBS_len(&protocol_name_list) == 0) {
+    return false;
+  }
+  while (CBS_len(&protocol_name_list) > 0) {
+    CBS protocol_name;
+    if (!CBS_get_u8_length_prefixed(&protocol_name_list, &protocol_name) ||
+        // Empty protocol names are forbidden.
+        CBS_len(&protocol_name) == 0) {
+      return false;
+    }
+  }
+  return true;
+}
+
 bool ssl_is_alpn_protocol_allowed(const SSL_HANDSHAKE *hs,
                                   Span<const uint8_t> protocol) {
   if (hs->config->alpn_client_proto_list.empty()) {
@@ -1580,25 +1596,12 @@
   CBS protocol_name_list;
   if (!CBS_get_u16_length_prefixed(&contents, &protocol_name_list) ||
       CBS_len(&contents) != 0 ||
-      CBS_len(&protocol_name_list) < 2) {
+      !ssl_is_valid_alpn_list(protocol_name_list)) {
     OPENSSL_PUT_ERROR(SSL, SSL_R_PARSE_TLSEXT);
     *out_alert = SSL_AD_DECODE_ERROR;
     return false;
   }
 
-  // Validate the protocol list.
-  CBS protocol_name_list_copy = protocol_name_list;
-  while (CBS_len(&protocol_name_list_copy) > 0) {
-    CBS protocol_name;
-    if (!CBS_get_u8_length_prefixed(&protocol_name_list_copy, &protocol_name) ||
-        // Empty protocol names are forbidden.
-        CBS_len(&protocol_name) == 0) {
-      OPENSSL_PUT_ERROR(SSL, SSL_R_PARSE_TLSEXT);
-      *out_alert = SSL_AD_DECODE_ERROR;
-      return false;
-    }
-  }
-
   const uint8_t *selected;
   uint8_t selected_len;
   int ret = ssl->ctx->alpn_select_cb(