diff --git a/src/epanet.c b/src/epanet.c
index b4027cb..7e7b994 100644
--- a/src/epanet.c
+++ b/src/epanet.c
@@ -1382,6 +1382,7 @@ int DLLEXPORT EN_setoption(EN_Project p, int option, double value)
         unit = ROUND(value);
         if (unit < 0 || unit > METERS) return 205;
         if (p->parser.Unitsflag == US && unit > PSI) return 0;
+        if (p->parser.Unitsflag == SI && unit == PSI) return 0;
         p->parser.Pressflag = unit;
         initunits(p);
         break;
diff --git a/tests/test_project.cpp b/tests/test_project.cpp
index c1635cd..6b102d3 100644
--- a/tests/test_project.cpp
+++ b/tests/test_project.cpp
@@ -183,6 +183,13 @@ BOOST_FIXTURE_TEST_CASE(test_pressure_units, FixtureInitClose)
     BOOST_REQUIRE(error == 0);
     BOOST_CHECK(abs(p - 298.76035) < 1.e-5);
 
+    // Set pressure to PSI and check that it remains in kPa
+    error = EN_setoption(ph, EN_PRESS_UNITS, EN_PSI);
+    BOOST_REQUIRE(error == 0);
+    error = EN_getoption(ph, EN_PRESS_UNITS, &units);
+    BOOST_REQUIRE(error == 0);
+    BOOST_CHECK(units == EN_KPA);
+
     error = EN_closeH(ph);
     BOOST_REQUIRE(error == 0);