diff --git a/fpvt.frm b/fpvt.frm
index b7c30ba..13c8a28 100644
--- a/fpvt.frm
+++ b/fpvt.frm
@@ -356,7 +356,11 @@ Private Sub UserForm_Activate()
     If (bVol + pVol) = 0 Then
         pPrc = 0
     Else
-        pPrc = (pVal + bVal) / (bVol + pVol) - bVal / bVol
+        If bVol = 0 Then
+            pPrc = 0
+        Else
+            pPrc = (pVal + bVal) / (bVol + pVol) - bVal / bVol
+        End If
     End If
     If aVal <> 0 Then
         MsgBox (aVal)