diff --git a/src/nn.h b/src/nn.h
index e6ed80c..b5056f5 100644
--- a/src/nn.h
+++ b/src/nn.h
@@ -64,7 +64,7 @@
 /*  www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html  */
 
 /*  The current interface version. */
-#define NN_VERSION_CURRENT 3
+#define NN_VERSION_CURRENT 4
 
 /*  The latest revision of the current interface. */
 #define NN_VERSION_REVISION 0