diff --git a/include/common/mem.h b/include/common/mem.h
index 4fd5b349..d0d5fdc5 100644
--- a/include/common/mem.h
+++ b/include/common/mem.h
@@ -44,6 +44,14 @@ void *xrealloc(void *ptr, size_t size);
  */
 char *xstrdup(const char *str);
 
+/*
+ * Same as ptr = xstrdup(str) but free
+ * <ptr> before assigning the result.
+ */
+#define xstrdup_replace(ptr, str) do { \
+	free(ptr); (ptr) = xstrdup(str); \
+} while (0)
+
 /*
  * Frees memory pointed to by <ptr> and sets <ptr> to NULL.
  * Does nothing if <ptr> is already NULL.