diff --git a/src/model/ControllerMechanicalVentilation.cpp b/src/model/ControllerMechanicalVentilation.cpp
index c70bcf1c437..d2ef137ed31 100644
--- a/src/model/ControllerMechanicalVentilation.cpp
+++ b/src/model/ControllerMechanicalVentilation.cpp
@@ -109,8 +109,13 @@ namespace model {
           if (oaSystem) {
             const auto airLoop = oaSystem->airLoopHVAC();
             if (airLoop) {
-              const auto sizingSystem = airLoop->sizingSystem();
-              result = sizingSystem.systemOutdoorAirMethod();
+              const auto sizingSystemOAMethod = airLoop->sizingSystem().systemOutdoorAirMethod();
+              const auto possible_vals = systemOutdoorAirMethodValues();
+              if (std::find_if(possible_vals.cbegin(), possible_vals.cend(),
+                               [&sizingSystemOAMethod](const std::string& val) { return openstudio::istringEqual(val, sizingSystemOAMethod); })
+                  != possible_vals.cend()) {
+                result = sizingSystemOAMethod;
+              }
             }
           }
         }
diff --git a/src/model/test/ControllerMechanicalVentilation_GTest.cpp b/src/model/test/ControllerMechanicalVentilation_GTest.cpp
index 7fc908c3654..ac9041fe865 100644
--- a/src/model/test/ControllerMechanicalVentilation_GTest.cpp
+++ b/src/model/test/ControllerMechanicalVentilation_GTest.cpp
@@ -12,6 +12,7 @@
 #include "../AirLoopHVACOutdoorAirSystem.hpp"
 #include "../DesignSpecificationOutdoorAir.hpp"
 #include "../Node.hpp"
+#include "../SizingSystem.hpp"
 #include "../Space.hpp"
 #include "../ThermalZone.hpp"
 
@@ -34,9 +35,42 @@ TEST_F(ModelFixture, ControllerMechanicalVentilation) {
 TEST_F(ModelFixture, ControllerMechanicalVentilation_SystemOutdoorAirMethod) {
 
   Model m;
-  ControllerMechanicalVentilation c(m);
-  EXPECT_TRUE(c.isSystemOutdoorAirMethodDefaulted());
-  EXPECT_EQ("Standard62.1VentilationRateProcedure", c.systemOutdoorAirMethod());
+  ControllerMechanicalVentilation controller_mv(m);
+  EXPECT_TRUE(controller_mv.isSystemOutdoorAirMethodDefaulted());
+  EXPECT_EQ("Standard62.1VentilationRateProcedure", controller_mv.systemOutdoorAirMethod());
+
+  ControllerOutdoorAir controller_oa(m);
+  EXPECT_TRUE(controller_oa.setControllerMechanicalVentilation(controller_mv));
+  EXPECT_TRUE(controller_mv.isSystemOutdoorAirMethodDefaulted());
+  EXPECT_EQ("Standard62.1VentilationRateProcedure", controller_mv.systemOutdoorAirMethod());
+
+  AirLoopHVACOutdoorAirSystem oa_system(m, controller_oa);
+  EXPECT_EQ("Standard62.1VentilationRateProcedure", controller_mv.systemOutdoorAirMethod());
+
+  AirLoopHVAC a(m);
+  auto sz = a.sizingSystem();
+
+  auto supplyInletNode = a.supplyInletNode();
+  EXPECT_TRUE(oa_system.addToNode(supplyInletNode));
+
+  // System Outdoor Air Method is common to both ControllerMechanicalVentilation and SizingSystem
+  EXPECT_TRUE(sz.setSystemOutdoorAirMethod("ZoneSum"));
+  EXPECT_TRUE(controller_mv.isSystemOutdoorAirMethodDefaulted());
+  EXPECT_EQ("ZoneSum", controller_mv.systemOutdoorAirMethod());
+
+  // System Outdoor Air Method is NOT common to both ControllerMechanicalVentilation and SizingSystem
+  EXPECT_TRUE(sz.setSystemOutdoorAirMethod("Standard62.1SimplifiedProcedure"));
+  EXPECT_TRUE(controller_mv.isSystemOutdoorAirMethodDefaulted());
+  EXPECT_EQ("Standard62.1VentilationRateProcedure", controller_mv.systemOutdoorAirMethod());
+
+  // Explicitly set the System Outdoor Air Method on the ControllerMechanicalVentilation
+  // => takes precedence over SizingSystem even if that method is common to both
+  EXPECT_TRUE(sz.setSystemOutdoorAirMethod("ZoneSum"));
+  EXPECT_TRUE(controller_mv.isSystemOutdoorAirMethodDefaulted());
+  EXPECT_EQ("ZoneSum", controller_mv.systemOutdoorAirMethod());
+  controller_mv.setSystemOutdoorAirMethod("ProportionalControlBasedOnOccupancySchedule");
+  EXPECT_FALSE(controller_mv.isSystemOutdoorAirMethodDefaulted());
+  EXPECT_EQ("ProportionalControlBasedOnOccupancySchedule", controller_mv.systemOutdoorAirMethod());
 }
 
 TEST_F(ModelFixture, ControllerMechanicalVentilation_hasZonesWithDesignSpecificationOutdoorAir) {