diff --git a/phreeqcpp/Phreeqc.h b/phreeqcpp/Phreeqc.h
index 30982a91..1b934e7a 100644
--- a/phreeqcpp/Phreeqc.h
+++ b/phreeqcpp/Phreeqc.h
@@ -1398,6 +1398,7 @@ protected:
 	*---------------------------------------------------------------------- */
 	std::vector<class unknown*> x;
 	size_t count_unknowns;
+	size_t sit_aqueous_unknowns;
 	size_t max_unknowns;
 
 	class unknown* ah2o_unknown;
diff --git a/phreeqcpp/prep.cpp b/phreeqcpp/prep.cpp
index f9d995ed..59df4ba1 100644
--- a/phreeqcpp/prep.cpp
+++ b/phreeqcpp/prep.cpp
@@ -1240,8 +1240,7 @@ build_model(void)
 	}
 	if (dl_type_x != cxxSurface::NO_DL && (/*pitzer_model == TRUE || */sit_model == TRUE)) //DL_pitz
 	{
-		error_msg("-diffuse_layer option not available for Pizer or SIT model",
-				  STOP);
+		warning_msg("-diffuse_layer option not tested for SIT model");
 	}
 /*
  *   Sum diffuse layer water into hydrogen and oxygen mass balances
@@ -1285,6 +1284,7 @@ build_model(void)
 			k++;
 			count_unknowns++;
 		}
+		sit_aqueous_unknowns = count_unknowns - j0;
 	}
 	/*
  *   Rewrite phases to current master species
diff --git a/phreeqcpp/sit.cpp b/phreeqcpp/sit.cpp
index 6268e450..27825c26 100644
--- a/phreeqcpp/sit.cpp
+++ b/phreeqcpp/sit.cpp
@@ -1117,7 +1117,8 @@ model_sit(void)
 			{
 				
 				count_basis_change++;
-				count_unknowns -= (int)this->s_x.size();
+				//count_unknowns -= (int)this->s_x.size();
+				count_unknowns -= sit_aqueous_unknowns;
 				reprep();
 				full_pitzer = false;
 			}