diff --git a/IPhreeqc.h b/IPhreeqc.h
index 4c04c426..62d99029 100644
--- a/IPhreeqc.h
+++ b/IPhreeqc.h
@@ -6,6 +6,10 @@
 
 #include "Var.h"
 
+#ifdef IPHREEQC_NO_FORTRAN_MODULE
+#include <stddef.h>
+#endif
+
 /**
  * @mainpage IPhreeqc Library Documentation (@PHREEQC_VER@-@REVISION_SVN@)
  *