diff --git a/models/Thumbnail.php b/models/Thumbnail.php
index c7c45ba5..5eb562c4 100644
--- a/models/Thumbnail.php
+++ b/models/Thumbnail.php
@@ -255,14 +255,18 @@ class Thumbnail
 				'_' . $this->width . 'x' . $this->height . $this->filename_suffix . '.' . $ext;
 
 			// Ensure the thumbnail subdirectory exists.
-			if (!is_dir(THUMBSDIR . '/' . $this->image->getSubdir()))
-				mkdir(THUMBSDIR . '/' . $this->image->getSubdir(), 0755, true);
+			$target_dir = THUMBSDIR . '/' . $this->image->getSubdir();
+			if (!is_dir($target_dir))
+				mkdir($target_dir, 0755, true);
+
+			if (!is_writable($target_dir))
+				throw new Exception('Thumbnail directory is not writable!');
 
 			// No need to preserve every detail.
 			$thumb->setImageCompressionQuality(80);
 
 			// Save it in a public spot.
-			$thumb->writeImage(THUMBSDIR . '/' . $this->image->getSubdir() . '/' . $thumb_filename);
+			$thumb->writeImage($target_dir . '/' . $thumb_filename);
 
 			// Let's remember this for future reference...
 			$this->markAsGenerated($thumb_filename);
@@ -273,7 +277,6 @@ class Thumbnail
 			// Finally, return the URL for the generated thumbnail image.
 			return THUMBSURL . '/' . $this->image->getSubdir() . '/' . $thumb_filename;
 		}
-		// Blast! Curse your sudden but inevitable betrayal!
 		catch (ImagickException $e)
 		{
 			throw new Exception('ImageMagick error occurred while generating thumbnail. Output: ' . $e->getMessage());
@@ -331,12 +334,11 @@ class Thumbnail
 		if ($success)
 		{
 			$thumb_selector = $this->width . 'x' . $this->height . $this->filename_suffix;
-			$this->thumbnails[$thumb_selector] = $filename !== 'NULL' ? $filename : '';
+			$this->thumbnails[$thumb_selector] = $filename !== 'NULL' ? $filename : null;
+			return $success;
 		}
 		else
 			throw new UnexpectedValueException('Thumbnail queuing query failed');
-
-		return $success;
 	}
 
 	private function markAsQueued()