diff --git a/docs/cli-reference.rst b/docs/cli-reference.rst
index 105b19a..5ea9200 100644
--- a/docs/cli-reference.rst
+++ b/docs/cli-reference.rst
@@ -321,6 +321,8 @@ See :ref:`cli_upsert`.
       incoming record has a primary key that matches an existing record the existing
       record will be updated.
 
+      If the table already exists and has a primary key, --pk can be omitted.
+
       Example:
 
           echo '[
@@ -330,7 +332,6 @@ See :ref:`cli_upsert`.
 
     Options:
       --pk TEXT                 Columns to use as the primary key, e.g. id
-                                [required]
       --flatten                 Flatten nested JSON objects, so {"a": {"b": 1}}
                                 becomes {"a_b": 1}
       --nl                      Expect newline-delimited JSON
diff --git a/docs/cli.rst b/docs/cli.rst
index bbbbf03..e373704 100644
--- a/docs/cli.rst
+++ b/docs/cli.rst
@@ -1593,6 +1593,8 @@ For example:
 
 This will update the dog with an ID of 2 to have an age of 4, creating a new record (with a null name) if one does not exist. If a row DOES exist the name will be left as-is.
 
+If the table already exists and has a primary key, you can omit the ``--pk`` option and ``sqlite-utils`` will use that existing primary key.
+
 The command will fail if you reference columns that do not exist on the table. To automatically create missing columns, use the ``--alter`` option.
 
 .. note::
diff --git a/sqlite_utils/cli.py b/sqlite_utils/cli.py
index 318b208..5e21f92 100644
--- a/sqlite_utils/cli.py
+++ b/sqlite_utils/cli.py
@@ -16,6 +16,7 @@ from sqlite_utils.db import (
     InvalidColumns,
     NoTable,
     NoView,
+    PrimaryKeyRequired,
     quote_identifier,
 )
 from sqlite_utils.plugins import ensure_plugins_loaded, pm, get_plugins
@@ -1184,7 +1185,7 @@ def insert_upsert_implementation(
             db.table(table).insert_all(
                 docs, pk=pk, batch_size=batch_size, alter=alter, **extra_kwargs
             )
-        except (NoTable, InvalidColumns) as e:
+        except (NoTable, InvalidColumns, PrimaryKeyRequired) as e:
             raise click.ClickException(str(e))
         except Exception as e:
             if (
@@ -1372,7 +1373,7 @@ def insert(
 
 
 @cli.command()
-@insert_upsert_options(require_pk=True)
+@insert_upsert_options()
 def upsert(
     path,
     table,
@@ -1408,6 +1409,8 @@ def upsert(
     an incoming record has a primary key that matches an existing record
     the existing record will be updated.
 
+    If the table already exists and has a primary key, --pk can be omitted.
+
     Example:
 
     \b
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 8196a08..bc5d492 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -1235,20 +1235,38 @@ def test_upsert(db_path, tmpdir):
     ]
 
 
-def test_upsert_pk_required(db_path, tmpdir):
+def test_upsert_pk_inferred_from_existing_table(db_path, tmpdir):
     json_path = str(tmpdir / "dogs.json")
+    db = Database(db_path)
     insert_dogs = [
         {"id": 1, "name": "Cleo", "age": 4},
         {"id": 2, "name": "Nixie", "age": 4},
     ]
     write_json(json_path, insert_dogs)
+    result = CliRunner().invoke(
+        cli.cli,
+        ["insert", db_path, "dogs", json_path, "--pk", "id"],
+        catch_exceptions=False,
+    )
+    assert result.exit_code == 0, result.output
+
+    write_json(
+        json_path,
+        [
+            {"id": 1, "age": 5},
+            {"id": 2, "age": 5},
+        ],
+    )
     result = CliRunner().invoke(
         cli.cli,
         ["upsert", db_path, "dogs", json_path],
         catch_exceptions=False,
     )
-    assert result.exit_code == 2
-    assert "Error: Missing option '--pk'" in result.output
+    assert result.exit_code == 0, result.output
+    assert list(db.query("select * from dogs order by id")) == [
+        {"id": 1, "name": "Cleo", "age": 5},
+        {"id": 2, "name": "Nixie", "age": 5},
+    ]
 
 
 def test_upsert_analyze(db_path, tmpdir):