diff --git a/changelog.d/14448.bugfix b/changelog.d/14448.bugfix
new file mode 100644
index 0000000000..4bf1c183f6
--- /dev/null
+++ b/changelog.d/14448.bugfix
@@ -0,0 +1 @@
+Fix rendering of some HTML templates (including emails). Introduced in v1.71.0.
diff --git a/synapse/res/templates/invalid_token.html b/synapse/res/templates/invalid_token.html
index d0b1dae669..b19e3023a1 100644
--- a/synapse/res/templates/invalid_token.html
+++ b/synapse/res/templates/invalid_token.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Invalid renewal token.{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/notif_mail.html b/synapse/res/templates/notif_mail.html
index 939d40315f..2add9dd859 100644
--- a/synapse/res/templates/notif_mail.html
+++ b/synapse/res/templates/notif_mail.html
@@ -1,3 +1,5 @@
+{% extends "_base.html" %}
+
 {% block title %}New activity in room{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/password_reset.html b/synapse/res/templates/password_reset.html
index de5a9ec68f..1f267946c8 100644
--- a/synapse/res/templates/password_reset.html
+++ b/synapse/res/templates/password_reset.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Password reset{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/password_reset_confirmation.html b/synapse/res/templates/password_reset_confirmation.html
index 0eac64b6a8..fabb9a6ed5 100644
--- a/synapse/res/templates/password_reset_confirmation.html
+++ b/synapse/res/templates/password_reset_confirmation.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Password reset confirmation{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/password_reset_failure.html b/synapse/res/templates/password_reset_failure.html
index 977babdb40..9990e860f9 100644
--- a/synapse/res/templates/password_reset_failure.html
+++ b/synapse/res/templates/password_reset_failure.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Password reset failure{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/password_reset_success.html b/synapse/res/templates/password_reset_success.html
index 0e99fad7ff..edada513ab 100644
--- a/synapse/res/templates/password_reset_success.html
+++ b/synapse/res/templates/password_reset_success.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Password reset success{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/recaptcha.html b/synapse/res/templates/recaptcha.html
index feaf3f6aed..8204928cdf 100644
--- a/synapse/res/templates/recaptcha.html
+++ b/synapse/res/templates/recaptcha.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Authentication{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/registration.html b/synapse/res/templates/registration.html
index 189960a832..cdb815665e 100644
--- a/synapse/res/templates/registration.html
+++ b/synapse/res/templates/registration.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Registration{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/registration_failure.html b/synapse/res/templates/registration_failure.html
index 3debe9301d..ae2a9cae2c 100644
--- a/synapse/res/templates/registration_failure.html
+++ b/synapse/res/templates/registration_failure.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Registration failure{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/registration_success.html b/synapse/res/templates/registration_success.html
index e2dd020a9e..6d45111796 100644
--- a/synapse/res/templates/registration_success.html
+++ b/synapse/res/templates/registration_success.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Your email has now been validated{% endblock %}
 
 {% block body %}
diff --git a/synapse/res/templates/registration_token.html b/synapse/res/templates/registration_token.html
index 2ee5866ba5..ee4e5295e7 100644
--- a/synapse/res/templates/registration_token.html
+++ b/synapse/res/templates/registration_token.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Authentication{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_account_deactivated.html b/synapse/res/templates/sso_account_deactivated.html
index c634229840..b85d96cc74 100644
--- a/synapse/res/templates/sso_account_deactivated.html
+++ b/synapse/res/templates/sso_account_deactivated.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}SSO account deactivated{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_auth_account_details.html b/synapse/res/templates/sso_auth_account_details.html
index b516333373..11636d7f5d 100644
--- a/synapse/res/templates/sso_auth_account_details.html
+++ b/synapse/res/templates/sso_auth_account_details.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Create your account{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_auth_bad_user.html b/synapse/res/templates/sso_auth_bad_user.html
index 69fdcc9ef0..819d79a461 100644
--- a/synapse/res/templates/sso_auth_bad_user.html
+++ b/synapse/res/templates/sso_auth_bad_user.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Authentication failed{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_auth_confirm.html b/synapse/res/templates/sso_auth_confirm.html
index 2d106e0ae4..3927d6eda3 100644
--- a/synapse/res/templates/sso_auth_confirm.html
+++ b/synapse/res/templates/sso_auth_confirm.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Confirm it's you{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_auth_success.html b/synapse/res/templates/sso_auth_success.html
index 56150eaefe..afeffb7191 100644
--- a/synapse/res/templates/sso_auth_success.html
+++ b/synapse/res/templates/sso_auth_success.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Authentication successful{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_error.html b/synapse/res/templates/sso_error.html
index e394a92623..6fa36c11c9 100644
--- a/synapse/res/templates/sso_error.html
+++ b/synapse/res/templates/sso_error.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Authentication failed{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_login_idp_picker.html b/synapse/res/templates/sso_login_idp_picker.html
index a2772ca9ef..58b0b3121c 100644
--- a/synapse/res/templates/sso_login_idp_picker.html
+++ b/synapse/res/templates/sso_login_idp_picker.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Choose identity provider{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_new_user_consent.html b/synapse/res/templates/sso_new_user_consent.html
index 126887d26c..fda29928d1 100644
--- a/synapse/res/templates/sso_new_user_consent.html
+++ b/synapse/res/templates/sso_new_user_consent.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Agree to terms and conditions{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/sso_redirect_confirm.html b/synapse/res/templates/sso_redirect_confirm.html
index 887ee0d294..cc2e7b3a5b 100644
--- a/synapse/res/templates/sso_redirect_confirm.html
+++ b/synapse/res/templates/sso_redirect_confirm.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Continue to your account{% endblock %}
 
 {% block header %}
diff --git a/synapse/res/templates/terms.html b/synapse/res/templates/terms.html
index 977c3d0bc7..ffabebdd8b 100644
--- a/synapse/res/templates/terms.html
+++ b/synapse/res/templates/terms.html
@@ -1,3 +1,4 @@
+{% extends "_base.html" %}
 {% block title %}Authentication{% endblock %}
 
 {% block header %}