diff --git a/src/PhpSpreadsheet/Reader/Xls.php b/src/PhpSpreadsheet/Reader/Xls.php
index 90bd5db69..816e7698d 100644
--- a/src/PhpSpreadsheet/Reader/Xls.php
+++ b/src/PhpSpreadsheet/Reader/Xls.php
@@ -430,7 +430,7 @@ class Xls extends BaseReader
      */
     public function canRead(string $filename): bool
     {
-        if (!File::testFileNoThrow($filename)) {
+        if (File::testFileNoThrow($filename) === false) {
             return false;
         }
 
@@ -440,6 +440,9 @@ class Xls extends BaseReader
 
             // get excel data
             $ole->read($filename);
+            if ($ole->wrkbook === null) {
+                throw new Exception('The filename ' . $filename . ' is not recognised as a Spreadsheet file');
+            }
 
             return true;
         } catch (PhpSpreadsheetException $e) {
@@ -449,7 +452,7 @@ class Xls extends BaseReader
 
     public function setCodepage(string $codepage): void
     {
-        if (!CodePage::validate($codepage)) {
+        if (CodePage::validate($codepage) === false) {
             throw new PhpSpreadsheetException('Unknown codepage: ' . $codepage);
         }
 
diff --git a/src/PhpSpreadsheet/Shared/OLERead.php b/src/PhpSpreadsheet/Shared/OLERead.php
index 3d952a9c8..fcc963953 100644
--- a/src/PhpSpreadsheet/Shared/OLERead.php
+++ b/src/PhpSpreadsheet/Shared/OLERead.php
@@ -134,7 +134,7 @@ class OLERead
 
         $bbdBlocks = $this->numBigBlockDepotBlocks;
 
-        if ($this->numExtensionBlocks != 0) {
+        if ($this->numExtensionBlocks !== 0) {
             $bbdBlocks = (self::BIG_BLOCK_SIZE - self::BIG_BLOCK_DEPOT_BLOCKS_POS) / 4;
         }
 
diff --git a/tests/PhpSpreadsheetTests/IOFactoryTest.php b/tests/PhpSpreadsheetTests/IOFactoryTest.php
index 19722dc7f..966a12629 100644
--- a/tests/PhpSpreadsheetTests/IOFactoryTest.php
+++ b/tests/PhpSpreadsheetTests/IOFactoryTest.php
@@ -108,6 +108,33 @@ class IOFactoryTest extends TestCase
         ];
     }
 
+    public function testIdentifyInvalid(): void
+    {
+        $file = __DIR__ . '/../data/Reader/NotASpreadsheetFile.doc';
+
+        $this->expectException(ReaderException::class);
+        $this->expectExceptionMessage('Unable to identify a reader for this file');
+        IOFactory::identify($file);
+    }
+
+    public function testCreateInvalid(): void
+    {
+        $file = __DIR__ . '/../data/Reader/NotASpreadsheetFile.doc';
+
+        $this->expectException(ReaderException::class);
+        $this->expectExceptionMessage('Unable to identify a reader for this file');
+        IOFactory::createReaderForFile($file);
+    }
+
+    public function testLoadInvalid(): void
+    {
+        $file = __DIR__ . '/../data/Reader/NotASpreadsheetFile.doc';
+
+        $this->expectException(ReaderException::class);
+        $this->expectExceptionMessage('Unable to identify a reader for this file');
+        IOFactory::load($file);
+    }
+
     public function testFormatAsExpected(): void
     {
         $fileName = 'samples/templates/30template.xls';
diff --git a/tests/data/Reader/NotASpreadsheetFile.doc b/tests/data/Reader/NotASpreadsheetFile.doc
new file mode 100644
index 000000000..10bf907ae
Binary files /dev/null and b/tests/data/Reader/NotASpreadsheetFile.doc differ