diff --git a/src/opngreduc/opngreduc.h b/src/opngreduc/opngreduc.h
index 82b12de..ac01f70 100644
--- a/src/opngreduc/opngreduc.h
+++ b/src/opngreduc/opngreduc.h
@@ -10,6 +10,7 @@
 #define OPNGREDUC_H
 
 #include "png.h"
+#include "string.h"
 
 
 #ifdef __cplusplus