diff --git a/requirements.in b/requirements.in
index e1f74f014..71207372d 100644
--- a/requirements.in
+++ b/requirements.in
@@ -15,7 +15,7 @@ iso8601==1.0.2
 itsdangerous==2.1.2
 jsonschema[format]==4.5.1
 marshmallow-sqlalchemy==0.23.1 # pyup: <0.24.0 # marshmallow v3 throws errors
-marshmallow==2.21.0 # pyup: <3 # v3 throws errors
+marshmallow==3.15.0
 psycopg2-binary==2.9.3
 PyJWT==2.4.0
 SQLAlchemy==1.4.36
diff --git a/requirements.txt b/requirements.txt
index 65eed3de6..bb154aa00 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -145,7 +145,7 @@ markupsafe==2.0.1
     # via
     #   jinja2
     #   mako
-marshmallow==2.21.0
+marshmallow==3.15.0
     # via
     #   -r requirements.in
     #   flask-marshmallow
@@ -161,7 +161,9 @@ notifications-utils @ git+https://github.com/alphagov/notifications-utils.git@55
 orderedset==2.0.3
     # via notifications-utils
 packaging==21.0
-    # via bleach
+    # via
+    #   bleach
+    #   marshmallow
 phonenumbers==8.12.36
     # via notifications-utils
 prometheus-client==0.14.1