diff --git a/panda/src/downloader/httpDigestAuthorization.cxx b/panda/src/downloader/httpDigestAuthorization.cxx
index 0b52e9957d..0059418298 100644
--- a/panda/src/downloader/httpDigestAuthorization.cxx
+++ b/panda/src/downloader/httpDigestAuthorization.cxx
@@ -21,6 +21,7 @@
 #ifdef HAVE_SSL
 
 #include <openssl/ssl.h>
+#include <openssl/md5.h>
 #include <time.h>
 
 const string HTTPDigestAuthorization::_mechanism = "digest";