diff --git a/src/coreclr/nativeaot/Runtime/CommonMacros.h b/src/coreclr/nativeaot/Runtime/CommonMacros.h
index e9e62638813ba..27f14f09eae4f 100644
--- a/src/coreclr/nativeaot/Runtime/CommonMacros.h
+++ b/src/coreclr/nativeaot/Runtime/CommonMacros.h
@@ -255,6 +255,10 @@ typedef uint8_t CODE_LOCATION;
     FCIMPL_RENAME_ARGSIZE(_rettype, _method, 24) \
     EXTERN_C _rettype F_CALL_CONV _method##_FCall (c, b, a) \
     {
+#define FCIMPL3_ILL(_rettype, _method, a, b, c) \
+    FCIMPL_RENAME_ARGSIZE(_rettype, _method, 20) \
+    EXTERN_C _rettype F_CALL_CONV _method##_FCall (a, c, b) \
+    {
 
 #else
 
@@ -289,6 +293,9 @@ typedef uint8_t CODE_LOCATION;
 #define FCIMPL3_DDD(_rettype, _method, a, b, c) \
     EXTERN_C _rettype F_CALL_CONV _method (a, b, c) \
     {
+#define FCIMPL3_ILL(_rettype, _method, a, b, c) \
+    EXTERN_C _rettype F_CALL_CONV _method (a, b, c) \
+    {
 
 #endif
 
diff --git a/src/coreclr/nativeaot/Runtime/MiscHelpers.cpp b/src/coreclr/nativeaot/Runtime/MiscHelpers.cpp
index d6c734bc0118a..c5bbcc2284277 100644
--- a/src/coreclr/nativeaot/Runtime/MiscHelpers.cpp
+++ b/src/coreclr/nativeaot/Runtime/MiscHelpers.cpp
@@ -423,7 +423,7 @@ FCIMPL3(int32_t, RhpLockCmpXchg32, int32_t * location, int32_t value, int32_t co
 }
 FCIMPLEND
 
-FCIMPL3(int64_t, RhpLockCmpXchg64, int64_t * location, int64_t value, int64_t comparand)
+FCIMPL3_ILL(int64_t, RhpLockCmpXchg64, int64_t * location, int64_t value, int64_t comparand)
 {
     return PalInterlockedCompareExchange64(location, value, comparand);
 }