diff --git a/src/pyipp/serializer.py b/src/pyipp/serializer.py
index 3a9df1b6..abdce6af 100644
--- a/src/pyipp/serializer.py
+++ b/src/pyipp/serializer.py
@@ -12,6 +12,19 @@
 
 _LOGGER = logging.getLogger(__name__)
 
+class UnsupportedAttributeError(RuntimeError):
+    """Some attribute name in a message is unsupported."""
+
+    def __init__(self, name: str) -> None:
+        """Initialize Exception with name of unsupported attribute."""
+        super(Exception, self).__init__(name)
+
+class DatatypeMismatchError(RuntimeError):
+    """Some attribute value has an unexpected data type."""
+
+    def __init__(self, msg: str) -> None:
+        """Initialize Exception with message."""
+        super(Exception, self).__init__(msg)
 
 def construct_attribute_values(tag: IppTag, value: Any) -> bytes:
     """Serialize the attribute values into IPP format."""
@@ -36,8 +49,7 @@ def construct_attribute(name: str, value: Any, tag: IppTag | None = None) -> byt
     byte_str = b""
 
     if not tag and not (tag := ATTRIBUTE_TAG_MAP.get(name, None)):
-        _LOGGER.debug("Unknown IppTag for %s", name)
-        return byte_str
+        raise UnsupportedAttributeError(name)
 
     if isinstance(value, (list, tuple, set)):
         for index, list_value in enumerate(value):
@@ -50,6 +62,25 @@ def construct_attribute(name: str, value: Any, tag: IppTag | None = None) -> byt
                 byte_str += struct.pack(">h", 0)
 
             byte_str += construct_attribute_values(tag, list_value)
+    elif isinstance(value, dict):
+        if tag != IppTag.BEGIN_COLLECTION:
+            msg = (f"Attribute {name} has data of type dict, but "
+                   f"its tag is not a collection but a {tag}")
+            raise DatatypeMismatchError(msg)
+        byte_str += struct.pack(">b", tag.value)  # value-tag
+        byte_str += struct.pack(">h", len(name))  # name-length
+        byte_str += name.encode("utf-8")          # name
+        byte_str += struct.pack(">h", 0)          # value-length
+        for k, v in value.items():
+            byte_str += struct.pack(">b", IppTag.MEMBER_NAME.value)  # value-tag
+            byte_str += struct.pack(">h", 0)       # name-length
+            byte_str += struct.pack(">h", len(k))  # value-length
+            byte_str += k.encode("utf-8")          # value (member-name)
+            byte_str += construct_attribute(k, v)
+        byte_str += struct.pack(">b", IppTag.END_COLLECTION.value)  # end-value-tag
+        byte_str += struct.pack(">h", 0)          # end-name-length
+        byte_str += struct.pack(">h", 0)          # end-value-length
+
     else:
         byte_str = struct.pack(">b", tag.value)
 
diff --git a/src/pyipp/tags.py b/src/pyipp/tags.py
index 9d03fba1..93dfd5da 100644
--- a/src/pyipp/tags.py
+++ b/src/pyipp/tags.py
@@ -31,6 +31,16 @@
     "job-uuid": IppTag.URI,
     "requested-attributes": IppTag.KEYWORD,
     "member-uris": IppTag.URI,
+    "media-col": IppTag.BEGIN_COLLECTION,
+    "media-size": IppTag.BEGIN_COLLECTION,
+    "media-bottom-margin": IppTag.INTEGER,
+    "media-left-margin": IppTag.INTEGER,
+    "media-right-margin": IppTag.INTEGER,
+    "x-dimension": IppTag.INTEGER,
+    "y-dimension": IppTag.INTEGER,
+    "media-source": IppTag.KEYWORD,
+    "media-top-margin": IppTag.INTEGER,
+    "media-type": IppTag.KEYWORD,
     "operations-supported": IppTag.ENUM,
     "ppd-name": IppTag.NAME,
     "printer-state-reason": IppTag.KEYWORD,
diff --git a/tests/test_serializer.py b/tests/test_serializer.py
index 410f8de8..51db1a76 100644
--- a/tests/test_serializer.py
+++ b/tests/test_serializer.py
@@ -1,5 +1,6 @@
 """Tests for Serializer."""
 from pyipp import serializer
+from pyipp import parser
 from pyipp.const import DEFAULT_CHARSET, DEFAULT_CHARSET_LANGUAGE, DEFAULT_PROTO_VERSION
 from pyipp.enums import IppOperation, IppTag
 
@@ -74,3 +75,47 @@ def test_encode_dict() -> None:
     assert result == load_fixture_binary(
         "serializer/get-printer-attributes-request-000.bin",
     )
+
+def test_encode_collections() -> None:
+    """Test encoding collections."""
+    message = {
+        "version": DEFAULT_PROTO_VERSION,
+        "operation": IppOperation.VALIDATE_JOB,
+        "request-id": 1,
+        "operation-attributes-tag": {
+            "attributes-charset": DEFAULT_CHARSET,
+            "attributes-natural-language": DEFAULT_CHARSET_LANGUAGE,
+            "requesting-user-name": "PythonIPP",
+            "printer-uri": "ipp://printer.example.com:361/ipp/print",
+        },
+        "job-attributes-tag": {
+            "media-col": {
+                "media-bottom-margin": 0,
+                "media-left-margin": 0,
+                "media-right-margin": 0,
+                "media-size": {
+                    "x-dimension": 10000,
+                    "y-dimension": 14800,
+                },
+                "media-source": "photo",
+                "media-top-margin": 0,
+                "media-type": "photographic",
+            },
+        },
+    }
+    encoded = serializer.encode_dict(message)
+    parsed = parser.parse(encoded)
+    assert parsed["jobs"] == [
+        {
+            "ipp-attribute-fidelity": True,
+            "media-col": {
+                "media-bottom-margin": 0,
+                "media-left-margin": 0,
+                "media-right-margin": 0,
+                "media-size": {"x-dimension": 10000, "y-dimension": 14800},
+                "media-source": "photo",
+                "media-top-margin": 0,
+                "media-type": "photographic",
+            },
+        },
+    ]