diff --git a/t_1.c b/t_1.c
index 33d1cc8..f19dfed 100644
--- a/t_1.c
+++ b/t_1.c
@@ -18,13 +18,21 @@
 #define R_SEQUENCE_NUMBER_MASK 0x10
 
 uint8_t NAD = 0x00;
-uint8_t PCB = 0x40; // Init to 0x40 so first call to next_pcb will return 0x00
+uint8_t dPCB = 0x40; // Init to 0x40 so first call to next_pcb will return 0x00
+uint8_t cPCB = 0x00; // Init to 0x40 so first call to next_pcb will return 0x00
+
+uint8_t seader_next_dpcb() {
+    uint8_t next_pcb = dPCB ^ 0x40;
+    FURI_LOG_D(TAG, "dPCB was: %02X, current dPCB: %02X", dPCB, next_pcb);
+    dPCB = next_pcb;
+    return dPCB;
+}
 
-uint8_t seader_next_pcb() {
-    uint8_t next_pcb = PCB ^ 0x40;
-    FURI_LOG_D(TAG, "PCB: %02X, Next PCB: %02X", PCB, next_pcb);
-    PCB = next_pcb;
-    return PCB;
+uint8_t seader_next_cpcb() {
+    uint8_t next_pcb = cPCB ^ 0x40;
+    FURI_LOG_D(TAG, "cPCB was: %02X, current cPCB: %02X", cPCB, next_pcb);
+    cPCB = next_pcb;
+    return cPCB;
 }
 
 void seader_t_1_set_IFSD(Seader* seader) {
@@ -51,15 +59,13 @@ void seader_t_1_send_ack(Seader* seader) {
     uint8_t frame_len = 0;
 
     frame[0] = NAD;
-    frame[1] = R_BLOCK | PCB;
+    frame[1] = R_BLOCK | dPCB;
     frame[2] = 0x00;
     frame_len = 3;
 
     frame_len = seader_add_lrc(frame, frame_len);
 
     FURI_LOG_D(TAG, "Sending R-Block ACK: PCB: %02x", frame[1]);
-    // Increment PCB
-    seader_next_pcb();
 
     seader_ccid_XfrBlock(seader_uart, frame, frame_len);
 }
@@ -82,9 +88,9 @@ void seader_send_t1(SeaderUartBridge* seader_uart, uint8_t* apdu, size_t len) {
 
         frame[0] = NAD;
         if(remaining > IFSC_VALUE) {
-            frame[1] = seader_next_pcb() | MORE_BIT;
+            frame[1] = seader_next_dpcb() | MORE_BIT;
         } else {
-            frame[1] = seader_next_pcb();
+            frame[1] = seader_next_dpcb();
         }
         frame[2] = copy_length;
         frame_len = 3;
@@ -116,7 +122,7 @@ void seader_send_t1(SeaderUartBridge* seader_uart, uint8_t* apdu, size_t len) {
     }
 
     frame[0] = NAD;
-    frame[1] = seader_next_pcb();
+    frame[1] = seader_next_dpcb();
     frame[2] = len;
     frame_len = 3;
 
@@ -154,7 +160,8 @@ bool seader_recv_t1(Seader* seader, CCID_Message* message) {
         return false;
     }
 
-    if(rPCB == PCB) {
+    if(rPCB == cPCB) {
+        seader_next_cpcb();
         if(seader_t_1_rx_buffer != NULL) {
             bit_buffer_append_bytes(seader_t_1_rx_buffer, message->payload + 3, LEN);
 
@@ -183,7 +190,7 @@ bool seader_recv_t1(Seader* seader, CCID_Message* message) {
             return true;
         }
         return seader_worker_process_sam_message(seader, message->payload, message->dwLength);
-    } else if(rPCB == (PCB | MORE_BIT)) {
+    } else if(rPCB == (cPCB | MORE_BIT)) {
         FURI_LOG_D(TAG, "Received T=1 frame with more bit set");
         if(seader_t_1_rx_buffer == NULL) {
             seader_t_1_rx_buffer = bit_buffer_alloc(512);
@@ -192,13 +199,22 @@ bool seader_recv_t1(Seader* seader, CCID_Message* message) {
         seader_t_1_send_ack(seader);
         return false;
     } else if((rPCB & R_BLOCK) == R_BLOCK) {
+        uint8_t R_SEQ = (rPCB & R_SEQUENCE_NUMBER_MASK) >> 4;
+        uint8_t I_SEQ = (dPCB ^ 0x40) >> 6;
+        if(R_SEQ != I_SEQ) {
+            FURI_LOG_D(
+                TAG,
+                "Received R-Block: Incorrect sequence.  Expected: %02X, Received: %02X",
+                I_SEQ,
+                R_SEQ);
+
+            return false;
+        }
+
         if(seader_t_1_tx_buffer != NULL) {
             // Send more data, re-using the buffer to trigger the code path that sends the next block
             SeaderWorker* seader_worker = seader->worker;
             SeaderUartBridge* seader_uart = seader_worker->uart;
-            // Move the R Block sequence bit to the I Block position
-            // PCB = (rPCB & R_SEQUENCE_NUMBER_MASK) << 2;
-            // FURI_LOG_D(TAG, "Received R-Block: sending next chunk. rPCB: %02x masked: %02x PCB: %02x", rPCB, (rPCB & R_SEQUENCE_NUMBER_MASK), PCB);
             seader_send_t1(
                 seader_uart,
                 (uint8_t*)bit_buffer_get_data(seader_t_1_tx_buffer),
@@ -207,7 +223,7 @@ bool seader_recv_t1(Seader* seader, CCID_Message* message) {
         }
     } else {
         FURI_LOG_W(
-            TAG, "Invalid T=1 frame: PCB mismatch.  Expected: %02X, Received: %02X", PCB, rPCB);
+            TAG, "Invalid T=1 frame: PCB mismatch.  Expected: %02X, Received: %02X", cPCB, rPCB);
     }
 
     return false;