diff --git a/boot/rtl/blrtl.cmake b/boot/rtl/blrtl.cmake
index 754116c5d3a..692727892b0 100644
--- a/boot/rtl/blrtl.cmake
+++ b/boot/rtl/blrtl.cmake
@@ -47,7 +47,8 @@ elseif(ARCH STREQUAL "amd64")
         ${NTOS_RTL_SOURCE_DIR}/byteswap.c
         ${NTOS_RTL_SOURCE_DIR}/mem.c)
 elseif(ARCH STREQUAL "arm")
-    list(APPEND ASM_SOURCE arm/debug_asm.S)
+    list(APPEND ASM_SOURCE
+        ${NTOS_RTL_SOURCE_DIR}/arm/debug_asm.S)
     list(APPEND SOURCE
         ${NTOS_RTL_SOURCE_DIR}/byteswap.c
         ${NTOS_RTL_SOURCE_DIR}/mem.c)