diff --git a/tmk_core/protocol/ibmpc.cpp b/tmk_core/protocol/ibmpc.cpp
index 34b8458d..c3e4ccd9 100644
--- a/tmk_core/protocol/ibmpc.cpp
+++ b/tmk_core/protocol/ibmpc.cpp
@@ -326,15 +326,39 @@ inline void IBMPC::isr(void)
                     protocol = IBMPC_PROTOCOL_XT_IBM;
                     goto DONE;
                 }
-             }
+            }
             break;
         case 0b00010000:
         case 0b10010000:
         case 0b01010000:
         case 0b11010000:
             // AT-done
-            // TODO: parity check?
             isr_debug = isr_state;
+
+            // Detect AA with parity error for AT/XT Auto-Switching support
+            // https://github.com/tmk/tmk_keyboard/wiki/IBM-PC-Keyboard-Converter#atxt-auto-switching
+            // isr_state: st pr b7 b6   b5 b4 b3 b2 | b1 b0  0 *1    0  0  0  0
+            //            1 '0' 1  0    1  0  1  0  | 1  0   0 *1    0  0  0  0
+            if (isr_state == 0xAA90) {
+                error = IBMPC_ERR_PARITY_AA;
+                goto ERROR;
+            }
+
+            // parit bit check
+            {
+                // isr_state: st pr b7 b6   b5 b4 b3 b2 | b1 b0  0 *1    0  0  0  0
+                uint8_t p = (isr_state & 0x4000) ? 1 : 0;
+                p ^= (isr_state >> 6);
+                while (p & 0xFE) {
+                    p = (p >> 1) ^ (p & 0x01);
+                }
+
+                if (p == 0) {
+                    error = IBMPC_ERR_PARITY;
+                    goto ERROR;
+                }
+            }
+
             // stop bit check
             if (isr_state & 0x8000) {
                 protocol = IBMPC_PROTOCOL_AT;
@@ -373,7 +397,11 @@ DONE:
         // buffer overflow
         error = IBMPC_ERR_FULL;
     }
+    goto END;
 ERROR:
+    // inhibit: Use clock_lo() instead of inhibit() for ISR optimization
+    clock_lo();
+END:
     // clear for next data
     isr_state = 0x8000;
 NEXT:
diff --git a/tmk_core/protocol/ibmpc.hpp b/tmk_core/protocol/ibmpc.hpp
index e13f3ea0..7f94c140 100644
--- a/tmk_core/protocol/ibmpc.hpp
+++ b/tmk_core/protocol/ibmpc.hpp
@@ -79,7 +79,8 @@ POSSIBILITY OF SUCH DAMAGE.
 
 // Error numbers
 #define IBMPC_ERR_NONE        0
-#define IBMPC_ERR_RECV        0x00
+#define IBMPC_ERR_PARITY      0x01
+#define IBMPC_ERR_PARITY_AA   0x02
 #define IBMPC_ERR_SEND        0x10
 #define IBMPC_ERR_TIMEOUT     0x20
 #define IBMPC_ERR_FULL        0x40