diff --git a/pygmt/params/position.py b/pygmt/params/position.py
index 1f91382d1c6..06fb724e79b 100644
--- a/pygmt/params/position.py
+++ b/pygmt/params/position.py
@@ -186,6 +186,18 @@ def _validate(self):
                         description="reference point",
                         reason="Expect a valid 2-character justification code.",
                     )
+            case _:
+                raise GMTValueError(
+                    self.cstype,
+                    description="cstype",
+                    choices=[
+                        "mapcoords",
+                        "plotcoords",
+                        "boxcoords",
+                        "inside",
+                        "outside",
+                    ],
+                )
         # Validate the anchor if specified.
         if self.anchor is not None and self.anchor not in _valid_anchors:
             raise GMTValueError(
diff --git a/pygmt/tests/test_params_position.py b/pygmt/tests/test_params_position.py
index a9d67de36c5..7faaa2bb208 100644
--- a/pygmt/tests/test_params_position.py
+++ b/pygmt/tests/test_params_position.py
@@ -37,6 +37,8 @@ def test_params_position_invalid_location():
     """
     Test that invalid location inputs raise GMTValueError.
     """
+    with pytest.raises(GMTValueError):
+        Position((1, 2), cstype="invalid")
     with pytest.raises(GMTValueError):
         Position("invalid", cstype="mapcoords")
     with pytest.raises(GMTValueError):