diff --git a/lib/indexopts.c b/lib/indexopts.c
index 4a860858..2ffd1942 100644
--- a/lib/indexopts.c
+++ b/lib/indexopts.c
@@ -20,6 +20,10 @@
 
 #include "notmuch-private.h"
 
+struct _notmuch_indexopts {
+    _notmuch_crypto_t crypto;
+};
+
 notmuch_indexopts_t *
 notmuch_database_get_default_indexopts (notmuch_database_t *db)
 {
diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index e9ce74a4..3cc79bc4 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -711,9 +711,7 @@ _notmuch_thread_create (void *ctx,
 
 /* indexopts.c */
 
-struct _notmuch_indexopts {
-    _notmuch_crypto_t crypto;
-};
+struct _notmuch_indexopts;
 
 #define CONFIG_HEADER_PREFIX "index.header."