diff --git a/components/fpspreadsheet/source/common/fpsfunc.pas b/components/fpspreadsheet/source/common/fpsfunc.pas
index d6cc85943..81269663c 100644
--- a/components/fpspreadsheet/source/common/fpsfunc.pas
+++ b/components/fpspreadsheet/source/common/fpsfunc.pas
@@ -2840,6 +2840,11 @@ begin
     rtCell:
       begin
         cell := ArgToCell(Args[0]);
+        if cell = nil then
+        begin
+          Result := ErrorResult(errWrongType);
+          exit;
+        end;
         case cell^.ContentType of
           cctUTF8String: searchString := cell^.UTF8StringValue;
           cctNumber: numSearchValue := cell^.NumberValue;
diff --git a/components/fpspreadsheet/source/common/fpsutils.pas b/components/fpspreadsheet/source/common/fpsutils.pas
index 23e478258..0b29871ab 100644
--- a/components/fpspreadsheet/source/common/fpsutils.pas
+++ b/components/fpspreadsheet/source/common/fpsutils.pas
@@ -1296,14 +1296,16 @@ end;
   @returns @TRUE when the sheet name must be quoted, @FALSE otherwise
 -------------------------------------------------------------------------------}
 function SheetNameNeedsQuotes(ASheet: String): Boolean;
+const
+  FORMULA_CHARS = ['+', '-', '*', '/', '^'];
 var
   i: Integer;
 begin
   if ASheet <> '' then begin
     Result := true;
-    if (ASheet[1] in ['0'..'9', '.']) then exit;
+    if (ASheet[1] in (['0'..'9', '.'] + FORMULA_CHARS)) then exit;
     for i := 1 to Length(ASheet) do
-      if (ASheet[i] in [' ', '<', '>', '=']) then exit;
+      if (ASheet[i] in ([' ', '<', '>', '='] + FORMULA_CHARS)) then exit;
   end;
   Result := false;
 end;