diff --git a/gsw_oceanographic_toolbox.c b/gsw_oceanographic_toolbox.c
index 1bda1f3..2ad24d4 100644
--- a/gsw_oceanographic_toolbox.c
+++ b/gsw_oceanographic_toolbox.c
@@ -4269,8 +4269,13 @@ gsw_geo_strf_dyn_height_1(double *sa, double *ct, double *p, double p_ref,
         err = err || gsw_util_pchip_interp(p, ct, nz, p_i, ct_i, n_i);
         if (err) err = 6;
     }
+    else if (interp_method == INTERP_METHOD_MRST) {
+        err = gsw_sa_ct_interp(sa, ct, p, nz,
+                               p_i, n_i, sa_i, ct_i);
+        if (err) err = 7;
+    }
     else {
-        err = 7;
+        err = 8;
     }
     if (err) {
         free(p_i);
diff --git a/gswteos-10.h b/gswteos-10.h
index e273cad..4fb1e76 100644
--- a/gswteos-10.h
+++ b/gswteos-10.h
@@ -35,6 +35,7 @@ extern "C" {
 
 #define INTERP_METHOD_LINEAR 1
 #define INTERP_METHOD_PCHIP 2
+#define INTERP_METHOD_MRST 3
 
 /*
 **  Prototypes: