diff --git a/src/include/const.h b/src/include/const.h
index c03df6849..88281c886 100644
--- a/src/include/const.h
+++ b/src/include/const.h
@@ -10,6 +10,8 @@ Author: 1985 Thomas L. Quarles
 #define CHARGE (1.6021918e-19)
 #define CONSTCtoK (273.15)
 #define CONSTboltz (1.3806226e-23)
+#define CONSTepsZero (8.854214871e-12)   /* epsilon zero F/m */
+#define CONSTepsSiO2 (3.4531479969e-11)  /* epsilon SiO2 F/m */
 #define REFTEMP 300.15 /* 27 degrees C */
 
     extern double CONSTroot2;
diff --git a/src/include/defines.h b/src/include/defines.h
index 117c162c4..cee4f19c6 100644
--- a/src/include/defines.h
+++ b/src/include/defines.h
@@ -62,6 +62,9 @@
 #define CHARGE (1.6021918e-19)
 #define CONSTCtoK (273.15)
 #define CONSTboltz (1.3806226e-23)
+#define CONSTepsZero (8.854214871e-12)   /* epsilon zero F/m */
+#define CONSTepsSiO2 (3.4531479969e-11)  /* epsilon SiO2 F/m */
+
 #define REFTEMP 300.15 /* 27 degrees C */