diff --git a/changes/bug31343 b/changes/bug31343
new file mode 100644
index 0000000000000000000000000000000000000000..17a8057eadf6f47ac01b06f845865faa968bea0a
--- /dev/null
+++ b/changes/bug31343
@@ -0,0 +1,9 @@
+  o Minor bugfixes (compilation):
+    - Avoid using labs() on time_t, which can cause compilation warnings
+      on 64-bit Windows builds.  Fixes bug 31343; bugfix on 0.2.4.4-alpha.
+
+  o Minor bugfixes (clock skew detection):
+    - Don't believe clock skew results from NETINFO cells that appear to
+      arrive before the VERSIONS cells they are responding to were sent.
+      Previously, we would accept them up to 3 minutes "in the past".
+      Fixes bug 31343; bugfix on 0.2.4.4-alpha.
diff --git a/src/or/channeltls.c b/src/or/channeltls.c
index 3a352d47feca42926096ccf6456872c425702f53..d44f7191384320c76edb502b6d4ad2bd47b08664 100644
--- a/src/or/channeltls.c
+++ b/src/or/channeltls.c
@@ -1583,6 +1583,18 @@ channel_tls_process_versions_cell(var_cell_t *cell, channel_tls_t *chan)
   }
 }
 
+/**
+ * Helper: compute the absolute value of a time_t.
+ *
+ * (we need this because labs() doesn't always work for time_t, since
+ * long can be shorter than time_t.)
+ */
+static inline time_t
+time_abs(time_t val)
+{
+  return (val < 0) ? -val : val;
+}
+
 /**
  * Process a 'netinfo' cell
  *
@@ -1601,7 +1613,7 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan)
   uint8_t n_other_addrs;
   time_t now = time(NULL);
 
-  long apparent_skew = 0;
+  time_t apparent_skew = 0;
   tor_addr_t my_apparent_addr = TOR_ADDR_NULL;
 
   tor_assert(cell);
@@ -1659,7 +1671,11 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan)
 
   /* Decode the cell. */
   timestamp = ntohl(get_uint32(cell->payload));
-  if (labs(now - chan->conn->handshake_state->sent_versions_at) < 180) {
+  const time_t sent_versions_at =
+    chan->conn->handshake_state->sent_versions_at;
+  if (now > sent_versions_at && (now - sent_versions_at) < 180) {
+    /* If we have gotten the NETINFO cell reasonably soon after having
+     * sent our VERSIONS cell, maybe we can learn skew information from it. */
     apparent_skew = now - timestamp;
   }
 
@@ -1705,7 +1721,7 @@ channel_tls_process_netinfo_cell(cell_t *cell, channel_tls_t *chan)
   /* Act on apparent skew. */
   /** Warn when we get a netinfo skew with at least this value. */
 #define NETINFO_NOTICE_SKEW 3600
-  if (labs(apparent_skew) > NETINFO_NOTICE_SKEW &&
+  if (time_abs(apparent_skew) > NETINFO_NOTICE_SKEW &&
       router_get_by_id_digest(chan->conn->identity_digest)) {
     int trusted = router_digest_is_trusted_dir(chan->conn->identity_digest);
     clock_skew_warning(TO_CONN(chan->conn), apparent_skew, trusted, LD_GENERAL,
@@ -2182,4 +2198,3 @@ channel_tls_process_authenticate_cell(var_cell_t *cell, channel_tls_t *chan)
 
 #undef ERR
 }
-
diff --git a/src/or/routerlist.c b/src/or/routerlist.c
index f73ec9baa126afb5b733e508b81a0357eb65e16a..f3b298006cdc0a5f12545165952ff88acdbc7f5d 100644
--- a/src/or/routerlist.c
+++ b/src/or/routerlist.c
@@ -5443,7 +5443,7 @@ int
 router_differences_are_cosmetic(const routerinfo_t *r1, const routerinfo_t *r2)
 {
   time_t r1pub, r2pub;
-  long time_difference;
+  time_t time_difference;
   tor_assert(r1 && r2);
 
   /* r1 should be the one that was published first. */
@@ -5506,7 +5506,9 @@ router_differences_are_cosmetic(const routerinfo_t *r1, const routerinfo_t *r2)
    * give or take some slop? */
   r1pub = r1->cache_info.published_on;
   r2pub = r2->cache_info.published_on;
-  time_difference = labs(r2->uptime - (r1->uptime + (r2pub - r1pub)));
+  time_difference = r2->uptime - (r1->uptime + (r2pub - r1pub));
+  if (time_difference < 0)
+    time_difference = - time_difference;
   if (time_difference > ROUTER_ALLOW_UPTIME_DRIFT &&
       time_difference > r1->uptime * .05 &&
       time_difference > r2->uptime * .05)
@@ -5816,4 +5818,3 @@ refresh_all_country_info(void)
 
   nodelist_refresh_countries();
 }
-