diff --git a/calefaction/database.py b/calefaction/database.py
index 012b2f9..4297016 100644
--- a/calefaction/database.py
+++ b/calefaction/database.py
@@ -4,7 +4,7 @@ from datetime import datetime
 import random
 import sqlite3
 
-from flask import g
+from flask import current_app, g
 from werkzeug.local import LocalProxy
 
 __all__ = ["Database"]
@@ -62,6 +62,9 @@ class Database:
         period of time, or if their absolute age exceeds some number. We don't
         actually remove them until a bit after this time.
         """
+        if current_app.debug:
+            return  # Sessions don't expire in debug mode
+
         query = """DELETE FROM session WHERE
             strftime("%s", "now") - strftime("%s", session_created) >= {} OR
             strftime("%s", "now") - strftime("%s", session_touched) >= {}"""
@@ -71,6 +74,22 @@ class Database:
         with self._conn as conn:
             conn.execute(query.format(create_thresh, touch_thresh))
 
+    def _build_expiry_check(self):
+        """Build and return a snippet of SQL to check for valid sessions.
+
+        The SQL should be inserted in a WHERE clause. If debug mode is active,
+        we just return an empty string.
+        """
+        if current_app.debug:
+            return ""
+
+        check = """ AND
+            strftime("%s", "now") -
+                strftime("%s", session_created) < {} AND
+            strftime("%s", "now") -
+                strftime("%s", session_touched) < {}"""
+        return check.format(self.MAX_SESSION_AGE, self.MAX_SESSION_STALENESS)
+
     def new_session(self):
         """Allocate a new session in the database.
 
@@ -94,11 +113,7 @@ class Database:
             self._clear_old_sessions()
 
         query = """SELECT session_created FROM session
-            WHERE session_id = ? AND
-            strftime("%s", "now") - strftime("%s", session_created) < {} AND
-            strftime("%s", "now") - strftime("%s", session_touched) < {}"""
-        query = query.format(self.MAX_SESSION_AGE, self.MAX_SESSION_STALENESS)
-
+            WHERE session_id = ?""" + self._build_expiry_check()
         res = self._conn.execute(query, (sid,)).fetchall()
         if not res:
             return None
@@ -107,11 +122,7 @@ class Database:
     def read_session(self, sid):
         """Return the character associated with the given session, or None."""
         query = """SELECT session_character FROM session
-            WHERE session_id = ? AND
-            strftime("%s", "now") - strftime("%s", session_created) < {} AND
-            strftime("%s", "now") - strftime("%s", session_touched) < {}"""
-        query = query.format(self.MAX_SESSION_AGE, self.MAX_SESSION_STALENESS)
-
+            WHERE session_id = ?""" + self._build_expiry_check()
         res = self._conn.execute(query, (sid,)).fetchall()
         return res[0][0] if res else None