diff --git a/CMakeLists.txt b/CMakeLists.txt
index bfb0bf933f8..ae87eb1e9f7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -331,12 +331,14 @@ zephyr_cc_option_ifdef(CONFIG_STACK_USAGE            -fstack-usage)
 # in binaries, makes failure logs more deterministic and most
 # importantly makes builds more deterministic
 
-# If both match then the last one wins. This matters for tests/ and
-# samples/ inside *both* CMAKE_SOURCE_DIR and ZEPHYR_BASE: for them
-# let's strip the shortest prefix.
+# If several match then the last one wins. This matters for instances
+# like tests/ and samples/: they're inside all of them! Then let's
+# strip as little as possible.
 zephyr_cc_option(-fmacro-prefix-map=${CMAKE_SOURCE_DIR}=CMAKE_SOURCE_DIR)
 zephyr_cc_option(-fmacro-prefix-map=${ZEPHYR_BASE}=ZEPHYR_BASE)
-# TODO: -fmacro-prefix-map=modules/etc. "build/zephyr_modules.txt" might help.
+if(WEST_TOPDIR)
+  zephyr_cc_option(-fmacro-prefix-map=${WEST_TOPDIR}=WEST_TOPDIR)
+endif()
 
 # TODO: Archiver arguments
 # ar_option(D)
diff --git a/cmake/host-tools.cmake b/cmake/host-tools.cmake
index 489bcecf00a..050bb90e2b9 100644
--- a/cmake/host-tools.cmake
+++ b/cmake/host-tools.cmake
@@ -37,6 +37,14 @@ else()
   # Just output information for a single version. This will still work
   # even after output is one line.
   message(STATUS "Found west: ${WEST} (found suitable version \"${west_version}\", minimum required is \"${MIN_WEST_VERSION}\")")
+
+  if (${west_version} VERSION_GREATER_EQUAL "0.7.0")
+    execute_process(
+      COMMAND ${WEST}  topdir
+      OUTPUT_VARIABLE  WEST_TOPDIR
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+      )
+  endif()
 endif()
 
 # Search for the must-have program dtc on PATH and in