diff --git a/xtoskrnl/includes/rtli.h b/xtoskrnl/includes/rtli.h
index 8457e68..616806d 100644
--- a/xtoskrnl/includes/rtli.h
+++ b/xtoskrnl/includes/rtli.h
@@ -221,7 +221,7 @@ RtlCountLeadingZeroes32(IN ULONG Value);
 
 XTAPI
 INT
-RtlCountLeadingZeroes64(IN ULONG Value);
+RtlCountLeadingZeroes64(IN ULONGLONG Value);
 
 XTAPI
 INT
diff --git a/xtoskrnl/rtl/math.c b/xtoskrnl/rtl/math.c
index 6261e93..f6003b4 100644
--- a/xtoskrnl/rtl/math.c
+++ b/xtoskrnl/rtl/math.c
@@ -81,7 +81,7 @@ RtlCountLeadingZeroes32(IN ULONG Value)
  */
 XTAPI
 INT
-RtlCountLeadingZeroes64(IN ULONG Value)
+RtlCountLeadingZeroes64(IN ULONGLONG Value)
 {
     /* Return a number of leading zero bits */
     return __builtin_clzll(Value);