diff --git a/json_row_test.go b/json_row_test.go
index 09ac830..9b8c16e 100644
--- a/json_row_test.go
+++ b/json_row_test.go
@@ -20,6 +20,7 @@ func TestJSONRow_MarshalJSON(t *testing.T) {
 		{"empty", row(t, R{}), toJSON(t, R{})},
 		{"single", row(t, R{"col1", 100}), toJSON(t, R{"col1", 100})},
 		{"multiple", row(t, R{"col1", 100, "col2", 10.5}), toJSON(t, R{"col1", 100, "col2", 10.5})},
+		{"duplicate column name", row(t, R{"col", "col"}), toJSON(t, R{"col", "col"})},
 	}
 
 	for _, tt := range cases {
@@ -43,6 +44,7 @@ func TestRows(t *testing.T) {
 		{"null", rows(t, nil), toJSON(t, nil)},
 		{"empties", rows(t, []R{{}, {}}), toJSON(t, []R{{}, {}})},
 		{"singles", rows(t, []R{{"col1", 100}, {"col1", 200}}), toJSON(t, []R{{"col1", 100}, {"col1", 200}})},
+		{"duplicate column name", rows(t, []R{{"col", "col"}}), toJSON(t, []R{{"col", "col"}})},
 	}
 
 	for _, tt := range cases {
diff --git a/writer_test.go b/writer_test.go
index b4489f1..1f5d110 100644
--- a/writer_test.go
+++ b/writer_test.go
@@ -34,6 +34,7 @@ func TestWriter_Write(t *testing.T) {
 		{"empty", row(t, R{}), []string{}, false},
 		{"single", row(t, R{"col1", 100}), []string{"100"}, false},
 		{"multiple", row(t, R{"col1", 100, "col2", 10.5}), []string{"100", "10.5"}, false},
+		{"duplicate column name", row(t, R{"col", 100, "col", 10.5}), []string{"100", "10.5"}, false},
 	}
 
 	for _, tt := range cases {