diff --git a/src/constants.h b/src/constants.h
index 77d76bf..1bada49 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -17,6 +17,10 @@
 #endif
 #endif
 
+#ifndef GSL_CONST_CGSM_GAUSS
+#define GSL_CONST_CGSM_GAUSS (1e0) /* g / abamp s^2 */
+#endif
+
 #ifdef HAVE_R
 #include <R.h>
 #include <Rmath.h>