diff --git a/ssl/test/runner/common.go b/ssl/test/runner/common.go
index 57b7b295..648807fc 100644
--- a/ssl/test/runner/common.go
+++ b/ssl/test/runner/common.go
@@ -842,6 +842,14 @@ type ProtocolBugs struct {
 	// SendSCTListOnResume, if not nil, causes the server to send the
 	// supplied SCT list in resumption handshakes.
 	SendSCTListOnResume []byte
+
+	// CECPQ1BadX25519Part corrupts the X25519 part of a CECPQ1 key exchange, as
+	// a trivial proof that it is actually used.
+	CECPQ1BadX25519Part bool
+
+	// CECPQ1BadNewhopePart corrupts the Newhope part of a CECPQ1 key exchange,
+	// as a trivial proof that it is actually used.
+	CECPQ1BadNewhopePart bool
 }
 
 func (c *Config) serverInit() {
diff --git a/ssl/test/runner/key_agreement.go b/ssl/test/runner/key_agreement.go
index 9a9962bf..5e5d976d 100644
--- a/ssl/test/runner/key_agreement.go
+++ b/ssl/test/runner/key_agreement.go
@@ -732,6 +732,16 @@ func (ka *cecpq1KeyAgreement) generateServerKeyExchange(config *Config, cert *Ce
 		return nil, err
 	}
 
+	if config.Bugs.CECPQ1BadX25519Part {
+		publicKey[0] ^= 1
+	}
+	if config.Bugs.CECPQ1BadNewhopePart {
+		publicKey[32] ^= 1
+		publicKey[33] ^= 1
+		publicKey[34] ^= 1
+		publicKey[35] ^= 1
+	}
+
 	var params []byte
 	params = append(params, byte(len(publicKey)>>8))
 	params = append(params, byte(len(publicKey)&0xff))
@@ -779,6 +789,16 @@ func (ka *cecpq1KeyAgreement) generateClientKeyExchange(config *Config, clientHe
 		return nil, nil, err
 	}
 
+	if config.Bugs.CECPQ1BadX25519Part {
+		publicKey[0] ^= 1
+	}
+	if config.Bugs.CECPQ1BadNewhopePart {
+		publicKey[32] ^= 1
+		publicKey[33] ^= 1
+		publicKey[34] ^= 1
+		publicKey[35] ^= 1
+	}
+
 	ckx := new(clientKeyExchangeMsg)
 	ckx.ciphertext = append(ckx.ciphertext, byte(len(publicKey)>>8))
 	ckx.ciphertext = append(ckx.ciphertext, byte(len(publicKey)&0xff))
diff --git a/ssl/test/runner/runner.go b/ssl/test/runner/runner.go
index 962ac019..8ea71725 100644
--- a/ssl/test/runner/runner.go
+++ b/ssl/test/runner/runner.go
@@ -5101,6 +5101,65 @@ func addCurveTests() {
 	})
 }
 
+func addCECPQ1Tests() {
+	testCases = append(testCases, testCase{
+		testType: clientTest,
+		name:     "CECPQ1-Client-BadX25519Part",
+		config: Config{
+			MinVersion:   VersionTLS12,
+			CipherSuites: []uint16{TLS_CECPQ1_RSA_WITH_AES_256_GCM_SHA384},
+			Bugs: ProtocolBugs{
+				CECPQ1BadX25519Part: true,
+			},
+		},
+		flags:              []string{"-cipher", "kCECPQ1"},
+		shouldFail:         true,
+		expectedLocalError: "local error: bad record MAC",
+	})
+	testCases = append(testCases, testCase{
+		testType: clientTest,
+		name:     "CECPQ1-Client-BadNewhopePart",
+		config: Config{
+			MinVersion:   VersionTLS12,
+			CipherSuites: []uint16{TLS_CECPQ1_RSA_WITH_AES_256_GCM_SHA384},
+			Bugs: ProtocolBugs{
+				CECPQ1BadNewhopePart: true,
+			},
+		},
+		flags:              []string{"-cipher", "kCECPQ1"},
+		shouldFail:         true,
+		expectedLocalError: "local error: bad record MAC",
+	})
+	testCases = append(testCases, testCase{
+		testType: serverTest,
+		name:     "CECPQ1-Server-BadX25519Part",
+		config: Config{
+			MinVersion:   VersionTLS12,
+			CipherSuites: []uint16{TLS_CECPQ1_RSA_WITH_AES_256_GCM_SHA384},
+			Bugs: ProtocolBugs{
+				CECPQ1BadX25519Part: true,
+			},
+		},
+		flags:         []string{"-cipher", "kCECPQ1"},
+		shouldFail:    true,
+		expectedError: ":DECRYPTION_FAILED_OR_BAD_RECORD_MAC:",
+	})
+	testCases = append(testCases, testCase{
+		testType: serverTest,
+		name:     "CECPQ1-Server-BadNewhopePart",
+		config: Config{
+			MinVersion:   VersionTLS12,
+			CipherSuites: []uint16{TLS_CECPQ1_RSA_WITH_AES_256_GCM_SHA384},
+			Bugs: ProtocolBugs{
+				CECPQ1BadNewhopePart: true,
+			},
+		},
+		flags:         []string{"-cipher", "kCECPQ1"},
+		shouldFail:    true,
+		expectedError: ":DECRYPTION_FAILED_OR_BAD_RECORD_MAC:",
+	})
+}
+
 func addKeyExchangeInfoTests() {
 	testCases = append(testCases, testCase{
 		name: "KeyExchangeInfo-RSA-Client",
@@ -5254,6 +5313,7 @@ func main() {
 	addCustomExtensionTests()
 	addRSAClientKeyExchangeTests()
 	addCurveTests()
+	addCECPQ1Tests()
 	addKeyExchangeInfoTests()
 	for _, async := range []bool{false, true} {
 		for _, splitHandshake := range []bool{false, true} {