diff --git a/deluge/plugins/blocklist/blocklist/core.py b/deluge/plugins/blocklist/blocklist/core.py
index 264f9f8f0..322eabc41 100644
--- a/deluge/plugins/blocklist/blocklist/core.py
+++ b/deluge/plugins/blocklist/blocklist/core.py
@@ -344,7 +344,7 @@ class Core(CorePluginBase):
         :raises UnknownFormatError: if the format cannot be detected
         """
         self.config["list_compression"] = detect_compression(blocklist)
-        self.config["list_type"] = detect_format(blocklist)
+        self.config["list_type"] = detect_format(blocklist, self.config["list_compression"])
         if not self.config["list_type"]:
             self.config["list_compression"] = ""
             raise UnknownFormatError
diff --git a/deluge/plugins/blocklist/blocklist/detect.py b/deluge/plugins/blocklist/blocklist/detect.py
index 9086bae09..67a8f9931 100644
--- a/deluge/plugins/blocklist/blocklist/detect.py
+++ b/deluge/plugins/blocklist/blocklist/detect.py
@@ -48,6 +48,6 @@ def detect_compression(filename):
     f.close()
     return COMPRESSION_TYPES.get(magic_number, "")
 
-def detect_format(filename):
+def detect_format(filename, compression=""):
     # TODO: implement this function
     return ""
diff --git a/deluge/plugins/blocklist/blocklist/readers.py b/deluge/plugins/blocklist/blocklist/readers.py
index 7624a3539..c8bf7aae2 100644
--- a/deluge/plugins/blocklist/blocklist/readers.py
+++ b/deluge/plugins/blocklist/blocklist/readers.py
@@ -60,6 +60,21 @@ class BaseReader(object):
         """Ignore commented lines and blank lines"""
         return line.startswith('#') or not line.strip()
 
+    def is_valid(self, file):
+        """Determines whether file is valid for this reader"""
+        blocklist = self.open()
+        valid = True
+        for line in blocklist:
+            if not self.is_ignored(line):
+                try:
+                    (start, end) = self.parse(line)
+                except:
+                    valid = False
+                finally:
+                    break
+        blocklist.close()
+        return valid
+
     def readranges(self):
         """Yields each ip range from the file"""
         blocklist = self.open()