diff --git a/command-line-arguments.c b/command-line-arguments.c
index 3aa87aa5..e7114143 100644
--- a/command-line-arguments.c
+++ b/command-line-arguments.c
@@ -13,7 +13,7 @@
 static notmuch_bool_t
 _process_keyword_arg (const notmuch_opt_desc_t *arg_desc, const char *arg_str) {
 
-    notmuch_keyword_t *keywords = arg_desc->keywords;
+    const notmuch_keyword_t *keywords = arg_desc->keywords;
 
     while (keywords->name) {
 	if (strcmp (arg_str, keywords->name) == 0) {
diff --git a/command-line-arguments.h b/command-line-arguments.h
index af8b1ceb..de1734ad 100644
--- a/command-line-arguments.h
+++ b/command-line-arguments.h
@@ -38,7 +38,7 @@ typedef struct notmuch_opt_desc {
     void *output_var;
     const char *name;
     int  arg_id;
-    struct notmuch_keyword *keywords;
+    const struct notmuch_keyword *keywords;
 } notmuch_opt_desc_t;