diff --git a/SDWebImage/SDDiskCache.m b/SDWebImage/SDDiskCache.m
index 539cd68b..bcad109d 100644
--- a/SDWebImage/SDDiskCache.m
+++ b/SDWebImage/SDDiskCache.m
@@ -135,7 +135,7 @@
                                                                   options:NSDirectoryEnumerationSkipsHiddenFiles
                                                              errorHandler:NULL];
     
-    NSDate *expirationDate = [NSDate dateWithTimeIntervalSinceNow:-self.config.maxCacheAge];
+    NSDate *expirationDate = (self.config.maxCacheAge < 0) ? nil: [NSDate dateWithTimeIntervalSinceNow:-self.config.maxCacheAge];
     NSMutableDictionary<NSURL *, NSDictionary<NSString *, id> *> *cacheFiles = [NSMutableDictionary dictionary];
     NSUInteger currentCacheSize = 0;
     
@@ -155,7 +155,7 @@
         
         // Remove files that are older than the expiration date;
         NSDate *modifiedDate = resourceValues[cacheContentDateKey];
-        if ([[modifiedDate laterDate:expirationDate] isEqualToDate:expirationDate]) {
+        if (expirationDate && [[modifiedDate laterDate:expirationDate] isEqualToDate:expirationDate]) {
             [urlsToDelete addObject:fileURL];
             continue;
         }
diff --git a/SDWebImage/SDImageCacheConfig.h b/SDWebImage/SDImageCacheConfig.h
index 3ac6fc7c..8732eaec 100644
--- a/SDWebImage/SDImageCacheConfig.h
+++ b/SDWebImage/SDImageCacheConfig.h
@@ -68,13 +68,14 @@ typedef NS_ENUM(NSUInteger, SDImageCacheConfigExpireType) {
 @property (assign, nonatomic) NSDataWritingOptions diskCacheWritingOptions;
 
 /**
- * The maximum length of time to keep an image in the cache, in seconds.
+ * The maximum length of time to keep an image in the disk cache, in seconds.
+ * Setting this to a negative value means no expiring.
  * Defaults to 1 weak.
  */
 @property (assign, nonatomic) NSTimeInterval maxCacheAge;
 
 /**
- * The maximum size of the cache, in bytes.
+ * The maximum size of the disk cache, in bytes.
  * Defaults to 0. Which means there is no cache size limit.
  */
 @property (assign, nonatomic) NSUInteger maxCacheSize;