diff --git a/src/ConverterHelpers.php b/src/ConverterHelpers.php
index dc412c2..4c194c0 100644
--- a/src/ConverterHelpers.php
+++ b/src/ConverterHelpers.php
@@ -10,7 +10,12 @@ class ConverterHelpers{
      */
     public static function RangeToColumnArray(string $range): array{
         $rangeArray = explode("-",$range);
-        if(count($rangeArray) !== 2){
+        if(count($rangeArray) !== 2 
+            || strlen($rangeArray[0]) === 0 
+            || strlen($rangeArray[1]) === 0 
+            || !(strlen($rangeArray[0]) < strlen($rangeArray[1]) 
+                || (strlen($rangeArray[0]) === strlen($rangeArray[1]) 
+                    && strcmp($rangeArray[0], $rangeArray[1]) <= 0))){
             throw new MalformattedRangeStringException();
         }
         
diff --git a/tests/ConverterHelpersTest.php b/tests/ConverterHelpersTest.php
index f86afe1..4b4e824 100644
--- a/tests/ConverterHelpersTest.php
+++ b/tests/ConverterHelpersTest.php
@@ -1,5 +1,6 @@
 <?php
 use CSO\Excel2Html\ConverterHelpers;
+use CSO\Excel2Html\Exceptions\MalformattedRangeStringException;
 use PHPUnit\Framework\TestCase;
 
 final class ConverterHelpersTest extends TestCase{
@@ -8,4 +9,16 @@ final class ConverterHelpersTest extends TestCase{
         $res = implode("|", $columns);
         $this->assertSame('Y|Z|AA|AB|AC', $res);
     }
+    public function testColumnRangeErrorOnWrongFormat(): void{
+        $this->expectException(MalformattedRangeStringException::class);
+        $columns = ConverterHelpers::RangeToColumnArray("-AC");
+    }
+    public function testColumnRangeErrorOnTwoLetterColumnFirst(): void{
+        $this->expectException(MalformattedRangeStringException::class);
+        $columns = ConverterHelpers::RangeToColumnArray("AC-Y");
+    }
+    public function testColumnRangeErrorOnHigherColumnFirst(): void{
+        $this->expectException(MalformattedRangeStringException::class);
+        $columns = ConverterHelpers::RangeToColumnArray("Z-B");
+    }
 }
\ No newline at end of file