diff --git a/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp b/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp
index 5520f7b..50394ac 100644
--- a/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp
@@ -190,7 +190,10 @@ bool CalibrationMeasurement::Base::canMeasureSimultaneously(std::set<Calibration
             break;
         case Type::Isolation:
             // Uses all ports, unable to measure simultaneously
-            return false;
+            if(measurements.size() > 1) {
+                return false;
+            }
+            break;
         case Type::Last:
             // invalid
             return false;