diff --git a/src/basic/string-util.c b/src/basic/string-util.c
index 105952156d..be42d5c4f5 100644
--- a/src/basic/string-util.c
+++ b/src/basic/string-util.c
@@ -830,7 +830,7 @@ char *strextend_with_separator_internal(char **x, const char *separator, ...) {
 
         need_separator = !isempty(*x);
 
-        nr = realloc(*x, l+1);
+        nr = realloc(*x, GREEDY_ALLOC_ROUND_UP(l+1));
         if (!nr)
                 return NULL;