diff --git a/classes/Optimization/File.php b/classes/Optimization/File.php
index 6173b204..7c2fb181 100644
--- a/classes/Optimization/File.php
+++ b/classes/Optimization/File.php
@@ -745,10 +745,9 @@ public function get_mime_type() {
 	/**
 	 * Get the file extension.
 	 *
-	 * @since  1.9
-	 * @author Grégory Viguier
+	 * @since 1.9
 	 *
-	 * @return string|null
+	 * @return string|false
 	 */
 	public function get_extension() {
 		return $this->get_file_type()->ext;
diff --git a/classes/Optimization/Process/AbstractProcess.php b/classes/Optimization/Process/AbstractProcess.php
index bc1868aa..afef4c47 100644
--- a/classes/Optimization/Process/AbstractProcess.php
+++ b/classes/Optimization/Process/AbstractProcess.php
@@ -581,7 +581,12 @@ public function optimize_size( $size, $optimization_level = null ) {
 			// This file type is not supported.
 			$extension = $file->get_extension();
 
-			if ( '' === $extension ) {
+			if ( ! $extension ) {
+				$response = new WP_Error(
+					'extension_not_mime',
+					__( 'This file has an extension that does not match a mime type.', 'imagify' )
+				);
+			} elseif ( '' === $extension ) {
 				$response = new WP_Error(
 					'no_extension',
 					__( 'With no extension, this file cannot be optimized.', 'imagify' )