diff --git a/Inventera.iss b/Inventera.iss
index e79fba5..66c66f7 100644
--- a/Inventera.iss
+++ b/Inventera.iss
@@ -166,8 +166,19 @@ end;
 
 function IsValidPort(const Value: String; var PortNumber: Integer): Boolean;
 begin
-  Result := TryStrToInt(Trim(Value), PortNumber) and
-    (PortNumber >= 1) and (PortNumber <= 65535);
+  Result := False;
+  PortNumber := 0;
+  if Trim(Value) = '' then
+    Exit;
+
+  try
+    PortNumber := StrToInt(Trim(Value));
+  except
+    PortNumber := 0;
+    Exit;
+  end;
+
+  Result := (PortNumber >= 1) and (PortNumber <= 65535);
 end;
 
 function IsValidIdentifier(const Value: String): Boolean;