diff --git a/nw/core/tools.py b/nw/core/tools.py
index c4455ff1..dd2c8c84 100644
--- a/nw/core/tools.py
+++ b/nw/core/tools.py
@@ -91,23 +91,25 @@ def countWords(theText):
 def numberToRoman(numVal, isLower=False):
     """Convert an integer to a roman number.
     """
-    if numVal < 1 or numVal > 4999:
+    if not isinstance(numVal, int):
         return "NAN"
+    if numVal < 1 or numVal > 4999:
+        return "OOR"
 
-    theValues  = [
+    theValues = [
         (1000, "M"), (900, "CM"), (500, "D"), (400, "CD"), (100, "C"), (90, "XC"),
         (50, "L"), (40, "XL"), (10, "X"), (9, "IX"), (5, "V"), (4, "IV"), (1, "I"),
     ]
 
     romNum = ""
     for theDiv, theSym in theValues:
-        for _ in range(numVal//theDiv):
-            romNum += theSym
-            numVal -= theDiv
+        n = numVal//theDiv
+        romNum += n*theSym
+        numVal -= n*theDiv
         if numVal <= 0:
             break
 
-    return romNum.lower if isLower else romNum
+    return romNum.lower() if isLower else romNum
 
 # =============================================================================================== #
 #  Convert an Integer to a Word Number
diff --git a/nw/gui/build.py b/nw/gui/build.py
index 7220639b..34a01f05 100644
--- a/nw/gui/build.py
+++ b/nw/gui/build.py
@@ -46,7 +46,7 @@ from PyQt5.QtWidgets import (
 
 from nw.common import fuzzyTime
 from nw.gui.custom import QSwitch
-from nw.core import ToHtml, numberToRoman
+from nw.core import ToHtml
 from nw.constants import (
     nwAlert, nwFiles, nwItemType, nwItemLayout, nwItemClass
 )
diff --git a/nw/gui/docviewer.py b/nw/gui/docviewer.py
index f20d9082..50c86b72 100644
--- a/nw/gui/docviewer.py
+++ b/nw/gui/docviewer.py
@@ -595,7 +595,7 @@ class GuiDocViewFooter(QWidget):
         self.showHide.setIconSize(QSize(fPx, fPx))
         self.showHide.setFixedSize(QSize(fPx, fPx))
         self.showHide.clicked.connect(self._doShowHide)
-        self.showHide.setToolTip("Show/hide the reference panel")
+        self.showHide.setToolTip("Show/hide the references panel")
 
         # Sticky Button
         stickyOn  = self.theTheme.getPixmap("sticky-on", (fPx, fPx))