diff --git a/imap-send.c b/imap-send.c
index d662811ee8..f2e1947e63 100644
--- a/imap-send.c
+++ b/imap-send.c
@@ -28,6 +28,7 @@
 #include "run-command.h"
 #include "parse-options.h"
 #include "setup.h"
+#include "strbuf.h"
 #if defined(NO_OPENSSL) && !defined(HAVE_OPENSSL_CSPRNG)
 typedef void *SSL;
 #endif