Index: firmware/App/Modes/ModeTreatment.c
===================================================================
diff -u -r408247fba0f81c8ca77fb3144694ac8d7358d87b -r52feec1100700c02663a4d02e2cb16bd48317c3a
--- firmware/App/Modes/ModeTreatment.c	(.../ModeTreatment.c)	(revision 408247fba0f81c8ca77fb3144694ac8d7358d87b)
+++ firmware/App/Modes/ModeTreatment.c	(.../ModeTreatment.c)	(revision 52feec1100700c02663a4d02e2cb16bd48317c3a)
@@ -1102,6 +1102,8 @@
     S32 txSecRem = CALC_TREAT_TIME_REMAINING_IN_SECS();
     S32 txMinEla = CALC_ELAPSED_TREAT_TIME_IN_SECS() / SEC_PER_MIN;
     F32 txMinRem = (F32)txSecRem / (F32)SEC_PER_MIN;
+    F32 colUFVol = getUltrafiltrationReferenceVolume();                                          // How much UF volume have we taken so far?
+    F32 remUFVol = uFVolume - colUFVol;                                                          // What would remaining UF volume be after subtracting UF volume already taken
 
     // Reset pending UF/time settings changes to current values in case request is rejected
     pendingUFVolumeChange = presMaxUFVolumeML;
@@ -1111,13 +1113,11 @@
     // Check if we are in an appropriate treatment state for settings adjustment
     if ( ( MODE_TREA == currMode ) &&
          ( currentTreatmentState > TREATMENT_START_STATE ) && ( currentTreatmentState < TREATMENT_END_STATE ) &&
-         ( uFVolume <= MAX_UF_VOLUME_ML ) &&
+         ( uFVolume <= MAX_UF_VOLUME_ML ) && ( remUFVol > MIN_UF_RATE_ML_MIN ) &&
          ( CALC_TREAT_TIME_REMAINING_IN_SECS() >= PREVENT_UF_VOL_CHANGE_IF_NEARLY_DONE_SEC ) )
     {
         DIALYSIS_STATE_T currDialysisState = getDialysisState();
         UF_STATE_T currUFState = getUltrafiltrationState();
-        F32 colUFVol = getUltrafiltrationReferenceVolume();                                          // How much UF volume have we taken so far?
-        F32 remUFVol = uFVolume - colUFVol;                                                          // What would remaining UF volume be after subtracting UF volume already taken
         F32 remUFVolCap = RANGE( remUFVol, 0.0F, (F32)MAX_UF_VOLUME_ML );                            // Enforce valid range on remaining UF volume
         F32 uFRate = remUFVolCap / txMinRem;                                                         // What UF rate would be if user selected to adjust it
         U32 trtTime = ( fabs( presUFRate ) < NEARLY_ZERO ? txMinEla + 1 : (S32)( remUFVolCap / presUFRate ) + txMinEla + 1 ); // What the treatment duration would be if user selected to adjust it
@@ -1165,7 +1165,8 @@
         {
             rejectReason = REQUEST_REJECT_REASON_INVALID_TREATMENT_STATE;
         }
-        else if ( uFVolume > MAX_UF_VOLUME_ML )
+        else if ( ( uFVolume > MAX_UF_VOLUME_ML ) ||
+                  ( remUFVol <= MIN_UF_RATE_ML_MIN ) )
         {
             rejectReason = REQUEST_REJECT_REASON_UF_VOLUME_OUT_OF_RANGE;
         }