diff --git a/nginx/modsecurity/ngx_http_modsecurity.c b/nginx/modsecurity/ngx_http_modsecurity.c
index edb26da8..e41ecb62 100644
--- a/nginx/modsecurity/ngx_http_modsecurity.c
+++ b/nginx/modsecurity/ngx_http_modsecurity.c
@@ -16,6 +16,8 @@
 #include <apr_bucket_nginx.h>
 #include <ngx_pool_context.h>
 
+#include <apr_base64.h>
+
 #undef CR
 #undef LF
 #undef CRLF