diff --git a/ssl/test/bssl_shim.cc b/ssl/test/bssl_shim.cc
index dabe5ec..fa0cb75 100644
--- a/ssl/test/bssl_shim.cc
+++ b/ssl/test/bssl_shim.cc
@@ -965,6 +965,9 @@
   if (config->tls_d5_bug) {
     SSL_set_options(ssl.get(), SSL_OP_TLS_D5_BUG);
   }
+  if (config->microsoft_big_sslv3_buffer) {
+    SSL_set_options(ssl.get(), SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER);
+  }
   if (config->no_legacy_server_connect) {
     SSL_clear_options(ssl.get(), SSL_OP_LEGACY_SERVER_CONNECT);
   }
@@ -1173,8 +1176,10 @@
     }
     if (!config->shim_shuts_down) {
       for (;;) {
-        uint8_t buf[512];
-        int n = DoRead(ssl.get(), buf, sizeof(buf));
+        uint8_t buf[16384];
+        // Read only 512 bytes at a time in TLS to ensure records may be
+        // returned in multiple reads.
+        int n = DoRead(ssl.get(), buf, config->is_dtls ? sizeof(buf) : 512);
         int err = SSL_get_error(ssl.get(), n);
         if (err == SSL_ERROR_ZERO_RETURN ||
             (n == 0 && err == SSL_ERROR_SYSCALL)) {
diff --git a/ssl/test/runner/common.go b/ssl/test/runner/common.go
index 2b7e29b..f578631 100644
--- a/ssl/test/runner/common.go
+++ b/ssl/test/runner/common.go
@@ -762,6 +762,10 @@
 	// shutdown. Records from the peer received after close_notify is sent
 	// are not discard.
 	ExpectCloseNotify bool
+
+	// SendLargeRecords, if true, allows outgoing records to be sent
+	// arbitrarily large.
+	SendLargeRecords bool
 }
 
 func (c *Config) serverInit() {
diff --git a/ssl/test/runner/conn.go b/ssl/test/runner/conn.go
index 42bc840..1b8700c 100644
--- a/ssl/test/runner/conn.go
+++ b/ssl/test/runner/conn.go
@@ -876,7 +876,7 @@
 	isClientHello := typ == recordTypeHandshake && len(data) > 0 && data[0] == typeClientHello
 	for len(data) > 0 || first {
 		m := len(data)
-		if m > maxPlaintext {
+		if m > maxPlaintext && !c.config.Bugs.SendLargeRecords {
 			m = maxPlaintext
 		}
 		if typ == recordTypeHandshake && c.config.Bugs.MaxHandshakeRecordLength > 0 && m > c.config.Bugs.MaxHandshakeRecordLength {
diff --git a/ssl/test/runner/runner.go b/ssl/test/runner/runner.go
index 7ada5f1..d085913 100644
--- a/ssl/test/runner/runner.go
+++ b/ssl/test/runner/runner.go
@@ -1984,6 +1984,47 @@
 				})
 			}
 		}
+
+		// Ensure both TLS and DTLS accept their maximum record sizes.
+		testCases = append(testCases, testCase{
+			name: suite.name + "-LargeRecord",
+			config: Config{
+				CipherSuites:         []uint16{suite.id},
+				Certificates:         []Certificate{cert},
+				PreSharedKey:         []byte(psk),
+				PreSharedKeyIdentity: pskIdentity,
+			},
+			flags:      flags,
+			messageLen: maxPlaintext,
+		})
+		testCases = append(testCases, testCase{
+			name: suite.name + "-LargeRecord-Extra",
+			config: Config{
+				CipherSuites:         []uint16{suite.id},
+				Certificates:         []Certificate{cert},
+				PreSharedKey:         []byte(psk),
+				PreSharedKeyIdentity: pskIdentity,
+				Bugs: ProtocolBugs{
+					SendLargeRecords: true,
+				},
+			},
+			flags:      append(flags, "-microsoft-big-sslv3-buffer"),
+			messageLen: maxPlaintext + 16384,
+		})
+		if isDTLSCipher(suite.name) {
+			testCases = append(testCases, testCase{
+				protocol: dtls,
+				name:     suite.name + "-LargeRecord-DTLS",
+				config: Config{
+					CipherSuites:         []uint16{suite.id},
+					Certificates:         []Certificate{cert},
+					PreSharedKey:         []byte(psk),
+					PreSharedKeyIdentity: pskIdentity,
+				},
+				flags:      flags,
+				messageLen: maxPlaintext,
+			})
+		}
 	}
 
 	testCases = append(testCases, testCase{
diff --git a/ssl/test/test_config.cc b/ssl/test/test_config.cc
index 4191b2b..edf3d6e 100644
--- a/ssl/test/test_config.cc
+++ b/ssl/test/test_config.cc
@@ -92,6 +92,7 @@
   { "-custom-extension-fail-add", &TestConfig::custom_extension_fail_add },
   { "-check-close-notify", &TestConfig::check_close_notify },
   { "-shim-shuts-down", &TestConfig::shim_shuts_down },
+  { "-microsoft-big-sslv3-buffer", &TestConfig::microsoft_big_sslv3_buffer },
 };
 
 const Flag<std::string> kStringFlags[] = {
diff --git a/ssl/test/test_config.h b/ssl/test/test_config.h
index c7bdab3..d6ccda2 100644
--- a/ssl/test/test_config.h
+++ b/ssl/test/test_config.h
@@ -89,6 +89,7 @@
   std::string ocsp_response;
   bool check_close_notify = false;
   bool shim_shuts_down = false;
+  bool microsoft_big_sslv3_buffer = false;
 };
 
 bool ParseConfig(int argc, char **argv, TestConfig *out_config);