diff --git a/configure.ac b/configure.ac
index e55cd2089..6950c7406 100644
--- a/configure.ac
+++ b/configure.ac
@@ -16,7 +16,7 @@
 # problem to the user.
 AC_PREREQ([2.59])
 
-m4_define([ngspice_major_version], [37])
+m4_define([ngspice_major_version], [37+])
 m4_define([ngspice_minor_version], [0])
 m4_define([ngspice_version],
       [ngspice_major_version])