diff --git a/posix/include/sof/lib/mailbox.h b/posix/include/sof/lib/mailbox.h
index 3d43a22e10ec..06e2659a5847 100644
--- a/posix/include/sof/lib/mailbox.h
+++ b/posix/include/sof/lib/mailbox.h
@@ -72,10 +72,6 @@ void mailbox_dspbox_read(void *dest, size_t dest_size,
 #define mailbox_hostbox_write(_offset, _src, _bytes) \
 	memcpy((char *)ipc->comp_data + _offset, _src, _bytes)
 
-static inline uint64_t mailbox_sw_reg_read64(uint32_t offset)
-{
-	return 0;
-}
 #else
 
 static inline
diff --git a/src/platform/library/include/platform/lib/mailbox.h b/src/platform/library/include/platform/lib/mailbox.h
index 04470a43e66e..daa858481149 100644
--- a/src/platform/library/include/platform/lib/mailbox.h
+++ b/src/platform/library/include/platform/lib/mailbox.h
@@ -59,6 +59,11 @@ static inline uint32_t mailbox_sw_reg_read(size_t offset)
 	return 0;
 }
 
+static inline uint64_t mailbox_sw_reg_read64(size_t offset)
+{
+	return 0;
+}
+
 #endif /* __PLATFORM_LIB_MAILBOX_H__ */
 
 #else