diff --git a/src/modules/jackrack/vst2_plugin.c b/src/modules/jackrack/vst2_plugin.c
index 009d871ba..fc3e9e2cb 100644
--- a/src/modules/jackrack/vst2_plugin.c
+++ b/src/modules/jackrack/vst2_plugin.c
@@ -22,6 +22,7 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include <ctype.h>
 #include <dlfcn.h>
 #include <ladspa.h>
 #include <stdio.h>