diff --git a/armsrc/hitagS.c b/armsrc/hitagS.c
index 00d204ce3..2f07a3468 100644
--- a/armsrc/hitagS.c
+++ b/armsrc/hitagS.c
@@ -889,9 +889,12 @@ void SimulateHitagSTag(bool tag_mem_supplied, uint8_t *data) {
     }
 
     tag.uid = ((tag.pages[0][3]) << 24) | ((tag.pages[0][2]) << 16) | ((tag.pages[0][1]) << 8) | tag.pages[0][0];
-    tag.key = ((tag.pages[3][3]) << 24) | ((tag.pages[3][2]) << 16) | ((tag.pages[3][1]) << 8) | tag.pages[3][0];
-    tag.key <<= 16;
-    tag.key += ((tag.pages[2][3]) << 8) + tag.pages[2][2];
+    tag.key = (((uint64_t)tag.pages[3][3]) << 40) |
+              (((uint64_t)tag.pages[3][2]) << 32) |
+              (((uint64_t)tag.pages[3][1]) << 24) |
+              (((uint64_t)tag.pages[3][0]) << 16) |
+              (((uint64_t)tag.pages[2][3]) << 8) |
+              (((uint64_t)tag.pages[2][2]));
     tag.pwdl0 = tag.pages[2][0];
     tag.pwdl1 = tag.pages[2][1];
     tag.pwdh0 = tag.pages[1][3];