diff --git a/adb/adb.cpp b/adb/adb.cpp
index 6b30be8..0e38897 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -240,7 +240,10 @@
     D("Calling send_connect");
     apacket* cp = get_apacket();
     cp->msg.command = A_CNXN;
-    cp->msg.arg0 = t->get_protocol_version();
+    // Send the max supported version, but because the transport is
+    // initialized to A_VERSION_MIN, this will be compatible with every
+    // device.
+    cp->msg.arg0 = A_VERSION;
     cp->msg.arg1 = t->get_max_payload();
 
     std::string connection_str = get_connection_string();
diff --git a/adb/adb.h b/adb/adb.h
index 3651413..21e5d4b 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -44,7 +44,12 @@
 #define A_AUTH 0x48545541
 
 // ADB protocol version.
-#define A_VERSION 0x01000000
+// Version revision:
+// 0x01000000: original
+// 0x01000001: skip checksum (Dec 2017)
+#define A_VERSION_MIN 0x01000000
+#define A_VERSION_SKIP_CHECKSUM 0x01000001
+#define A_VERSION 0x01000001
 
 // Used for help/version information.
 #define ADB_VERSION_MAJOR 1
@@ -53,7 +58,7 @@
 std::string adb_version();
 
 // Increment this when we want to force users to start a new adb server.
-#define ADB_SERVER_VERSION 39
+#define ADB_SERVER_VERSION 40
 
 using TransportId = uint64_t;
 class atransport;
diff --git a/adb/transport.cpp b/adb/transport.cpp
index 089a1ec..5cf2450 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -163,7 +163,12 @@
 
 void send_packet(apacket* p, atransport* t) {
     p->msg.magic = p->msg.command ^ 0xffffffff;
-    p->msg.data_check = calculate_apacket_checksum(p);
+    // compute a checksum for connection/auth packets for compatibility reasons
+    if (t->get_protocol_version() >= A_VERSION_SKIP_CHECKSUM) {
+        p->msg.data_check = 0;
+    } else {
+        p->msg.data_check = calculate_apacket_checksum(p);
+    }
 
     print_packet("send", p);
 
@@ -1089,10 +1094,6 @@
     return true;
 }
 
-bool check_data(apacket* p) {
-    return calculate_apacket_checksum(p) == p->msg.data_check;
-}
-
 #if ADB_HOST
 std::shared_ptr<RSA> atransport::NextKey() {
     if (keys_.empty()) keys_ = adb_auth_get_private_keys();
diff --git a/adb/transport.h b/adb/transport.h
index 8c101fd..86cd992 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -66,7 +66,9 @@
     atransport(ConnectionState state = kCsOffline)
         : id(NextTransportId()), connection_state_(state) {
         transport_fde = {};
-        protocol_version = A_VERSION;
+        // Initialize protocol to min version for compatibility with older versions.
+        // Version will be updated post-connect.
+        protocol_version = A_VERSION_MIN;
         max_payload = MAX_PAYLOAD;
     }
     virtual ~atransport() {}
@@ -223,7 +225,6 @@
 void unregister_usb_transport(usb_handle* usb);
 
 bool check_header(apacket* p, atransport* t);
-bool check_data(apacket* p);
 
 void close_usb_devices();
 void close_usb_devices(std::function<bool(const atransport*)> predicate);
diff --git a/adb/transport_local.cpp b/adb/transport_local.cpp
index 9cd378c..d6c84da 100644
--- a/adb/transport_local.cpp
+++ b/adb/transport_local.cpp
@@ -77,11 +77,6 @@
         return -1;
     }
 
-    if (!check_data(p)) {
-        D("bad data: terminated (data)");
-        return -1;
-    }
-
     return 0;
 }
 
diff --git a/adb/transport_usb.cpp b/adb/transport_usb.cpp
index c3ac344..3474820 100644
--- a/adb/transport_usb.cpp
+++ b/adb/transport_usb.cpp
@@ -109,10 +109,6 @@
             goto err_msg;
         }
     }
-    if (!check_data(p)) {
-        D("remote usb: check_data failed, skip it");
-        goto err_msg;
-    }
     return 0;
 
 err_msg:
@@ -143,11 +139,6 @@
         }
     }
 
-    if (!check_data(p)) {
-        LOG(ERROR) << "remote usb: check_data failed";
-        return -1;
-    }
-
     return 0;
 }
 #endif