diff --git a/ssl/custom_extensions.c b/ssl/custom_extensions.c
index 10fbfc8..ea57c20 100644
--- a/ssl/custom_extensions.c
+++ b/ssl/custom_extensions.c
@@ -69,6 +69,14 @@
     return 1;
   }
 
+  if (ssl->ctx->enable_early_data) {
+    /* TODO(svaldez): Support Custom Extensions with 0-RTT. For now the caller
+     * is expected not to configure both together.
+     * https://crbug.com/boringssl/173. */
+    OPENSSL_PUT_ERROR(SSL, SSL_R_CUSTOM_EXTENSION_ERROR);
+    return 0;
+  }
+
   for (size_t i = 0; i < sk_SSL_CUSTOM_EXTENSION_num(stack); i++) {
     const SSL_CUSTOM_EXTENSION *ext = sk_SSL_CUSTOM_EXTENSION_value(stack, i);
 
diff --git a/ssl/test/runner/runner.go b/ssl/test/runner/runner.go
index f7e39ab..05838d8 100644
--- a/ssl/test/runner/runner.go
+++ b/ssl/test/runner/runner.go
@@ -7878,6 +7878,22 @@
 			flags: []string{flag},
 		})
 
+		// 0-RTT is not currently supported with Custom Extensions.
+		testCases = append(testCases, testCase{
+			testType: testType,
+			name:     "CustomExtensions-" + suffix + "-EarlyData",
+			config: Config{
+				MaxVersion: VersionTLS13,
+				Bugs: ProtocolBugs{
+					CustomExtension:         expectedContents,
+					ExpectedCustomExtension: &expectedContents,
+				},
+			},
+			shouldFail:    true,
+			expectedError: ":CUSTOM_EXTENSION_ERROR:",
+			flags:         []string{flag, "-enable-early-data"},
+		})
+
 		// If the parse callback fails, the handshake should also fail.
 		testCases = append(testCases, testCase{
 			testType: testType,
@@ -10321,6 +10337,47 @@
 		},
 	})
 
+	// Test that we fail on early data with Channel ID.
+	testCases = append(testCases, testCase{
+		testType: clientTest,
+		name:     "TLS13-EarlyData-ChannelID-Client",
+		config: Config{
+			MaxVersion:       VersionTLS13,
+			MaxEarlyDataSize: 16384,
+			RequestChannelID: true,
+		},
+		resumeSession:   true,
+		expectChannelID: true,
+		shouldFail:      true,
+		expectedError:   ":CHANNEL_ID_ON_EARLY_DATA:",
+		flags: []string{
+			"-enable-early-data",
+			"-expect-early-data-info",
+			"-send-channel-id", path.Join(*resourceDir, channelIDKeyFile),
+		},
+	})
+
+	testCases = append(testCases, testCase{
+		testType: serverTest,
+		name:     "TLS13-EarlyData-ChannelID-Server",
+		config: Config{
+			MaxVersion: VersionTLS13,
+			ChannelID:  channelIDKey,
+			Bugs: ProtocolBugs{
+				SendEarlyData:           [][]byte{{}},
+				ExpectEarlyDataAccepted: false,
+			},
+		},
+		resumeSession:   true,
+		expectChannelID: true,
+		flags: []string{
+			"-enable-early-data",
+			"-expect-reject-early-data",
+			"-expect-channel-id",
+			base64.StdEncoding.EncodeToString(channelIDBytes),
+		},
+	})
+
 }
 
 func addTLS13CipherPreferenceTests() {
diff --git a/ssl/tls13_client.c b/ssl/tls13_client.c
index 9f586f5..0d60661 100644
--- a/ssl/tls13_client.c
+++ b/ssl/tls13_client.c
@@ -365,6 +365,10 @@
       OPENSSL_PUT_ERROR(SSL, SSL_R_ALPN_MISMATCH_ON_EARLY_DATA);
       return ssl_hs_error;
     }
+    if (ssl->s3->tlsext_channel_id_valid) {
+      OPENSSL_PUT_ERROR(SSL, SSL_R_CHANNEL_ID_ON_EARLY_DATA);
+      return ssl_hs_error;
+    }
   }
 
   /* Release offered session now that it is no longer needed. */
diff --git a/ssl/tls13_server.c b/ssl/tls13_server.c
index 5211dff..dbb44d2 100644
--- a/ssl/tls13_server.c
+++ b/ssl/tls13_server.c
@@ -359,6 +359,8 @@
           session->ticket_max_early_data != 0 &&
           /* The client must have offered early data. */
           hs->early_data_offered &&
+          /* Channel ID is incompatible with 0-RTT. */
+          !ssl->s3->tlsext_channel_id_valid &&
           /* The negotiated ALPN must match the one in the ticket. */
           ssl->s3->alpn_selected_len == session->early_alpn_len &&
           OPENSSL_memcmp(ssl->s3->alpn_selected, session->early_alpn,