diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9c772520d5..b0d0fc1e9c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -87,12 +87,6 @@ if(KernelArchRiscV)
     endif()
 endif()
 string(APPEND common_flags " ${build_arch}")
-if(Kernel64)
-    string(APPEND common_flags " -D__KERNEL_64__")
-else()
-    string(APPEND common_flags " -D__KERNEL_32__")
-endif()
-
 set(
     BASE_ASM_FLAGS "${asm_common_flags} ${common_flags}"
     CACHE INTERNAL "Default ASM flags for compilation \
diff --git a/include/fastpath/fastpath.h b/include/fastpath/fastpath.h
index 252c42f910..eb99885171 100644
--- a/include/fastpath/fastpath.h
+++ b/include/fastpath/fastpath.h
@@ -68,14 +68,16 @@ static inline void thread_state_ptr_mset_blockingObject_tsType(thread_state_t *t
 static inline void cap_reply_cap_ptr_new_np(cap_t *cap_ptr, word_t capReplyCanGrant,
                                             word_t capReplyMaster, word_t capTCBPtr)
 {
-#ifdef __KERNEL_64__
+#if CONFIG_WORD_SIZE == 64
     cap_ptr->words[1] = (word_t)capTCBPtr;
     cap_ptr->words[0] = (capReplyMaster) | (capReplyCanGrant << 1) |
                         ((word_t)cap_reply_cap << 59);
-#else
+#elif CONFIG_WORD_SIZE == 32
     cap_ptr->words[0] = TCB_REF(capTCBPtr) | (capReplyMaster << 4) |
                         (capReplyCanGrant << 5) | cap_reply_cap ;
-#endif
+#else
+#error invalid CONFIG_WORD_SIZE
+#endif /* CONFIG_WORD_SIZE */
 }
 #endif