diff --git a/respodns/ip_info.py b/respodns/ip_info.py
index ec1a380..8c08fdb 100644
--- a/respodns/ip_info.py
+++ b/respodns/ip_info.py
@@ -1,5 +1,4 @@
 from collections import namedtuple
-from sys import stderr
 from time import time
 
 CacheLine = namedtuple("CacheLine", ("time", "code"))
@@ -7,6 +6,11 @@ CacheLine = namedtuple("CacheLine", ("time", "code"))
 one_month = 365.25 / 12 * 24 * 60 * 60  # in seconds
 
 
+def mask_ip(ip):
+    # this assumes IP info is the same for a /24 subnet.
+    return ".".join(ip.split(".")[:3]) + ".0"
+
+
 class IpInfoBase:
     pass
 
@@ -172,7 +176,8 @@ class IpInfoByIpApi(IpInfoBase):
                     continue
                 ip, time, code = row[0], float(row[1]), row[2]
                 info = CacheLine(time, code)
-                self.stored[ip] = info
+                masked = mask_ip(ip)
+                self.stored[masked] = info
 
     def flush(self):
         from csv import writer
@@ -183,7 +188,8 @@ class IpInfoByIpApi(IpInfoBase):
             handle.writerow(self.csv_header)
             for ip, info in self.stored.items():
                 timestr = "{:.2f}".format(info.time)
-                handle.writerow([ip, timestr, info.code])
+                masked = mask_ip(ip)
+                handle.writerow([masked, timestr, info.code])
 
     def cache(self, ip, info=None, timestamp=None):
         if self.stored is None:
@@ -191,8 +197,10 @@ class IpInfoByIpApi(IpInfoBase):
 
         now = time() if timestamp is None else timestamp
 
+        masked = mask_ip(ip)
+
         if info is None:
-            cached = self.stored.get(ip, None)
+            cached = self.stored.get(masked, None)
             if cached is None:
                 return None
             if now > cached.time + self.expiry:
@@ -200,7 +208,7 @@ class IpInfoByIpApi(IpInfoBase):
             return cached
         else:
             assert isinstance(info, CacheLine), type(info)
-            self.stored[ip] = info
+            self.stored[masked] = info
 
     async def find_country(self, ip, db=None):
         now = time()