diff --git a/datasquare.go b/datasquare.go
index 5c6890d..5b82e01 100644
--- a/datasquare.go
+++ b/datasquare.go
@@ -135,6 +135,9 @@ func (ds *dataSquare) setRowSlice(x uint, y uint, newRow [][]byte) error {
 			return errors.New("invalid chunk size")
 		}
 	}
+	if y+uint(len(newRow)) > ds.width {
+		return fmt.Errorf("cannot set row slice at (%d, %d) of length %d: because it would exceed the data square width %d", x, y, len(newRow), ds.width)
+	}
 
 	ds.dataMutex.Lock()
 	defer ds.dataMutex.Unlock()
@@ -165,6 +168,9 @@ func (ds *dataSquare) setColSlice(x uint, y uint, newCol [][]byte) error {
 			return errors.New("invalid chunk size")
 		}
 	}
+	if x+uint(len(newCol)) > ds.width {
+		return fmt.Errorf("cannot set col slice at (%d, %d) of length %d: because it would exceed the data square width %d", x, y, len(newCol), ds.width)
+	}
 
 	ds.dataMutex.Lock()
 	defer ds.dataMutex.Unlock()
diff --git a/datasquare_test.go b/datasquare_test.go
index 0db5303..90b28a4 100644
--- a/datasquare_test.go
+++ b/datasquare_test.go
@@ -219,6 +219,120 @@ func TestDefaultTreeProofs(t *testing.T) {
 	}
 }
 
+func Test_setRowSlice(t *testing.T) {
+	type testCase struct {
+		name    string
+		newRow  [][]byte
+		x       uint
+		y       uint
+		want    [][]byte
+		wantErr bool
+	}
+	testCases := []testCase{
+		{
+			name:    "overwrite the first row",
+			newRow:  [][]byte{{5}, {6}},
+			x:       0,
+			y:       0,
+			want:    [][]byte{{5}, {6}, {3}, {4}},
+			wantErr: false,
+		},
+		{
+			name:    "overwrite the last row",
+			newRow:  [][]byte{{5}, {6}},
+			x:       1,
+			y:       0,
+			want:    [][]byte{{1}, {2}, {5}, {6}},
+			wantErr: false,
+		},
+		{
+			name:    "returns an error if the new row has an invalid chunk size",
+			newRow:  [][]byte{{5, 6}},
+			x:       0,
+			y:       0,
+			wantErr: true,
+		},
+		{
+			name:    "returns an error if the new row would surpass the data square's width",
+			newRow:  [][]byte{{5}, {6}},
+			x:       0,
+			y:       1,
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		ds, err := newDataSquare([][]byte{{1}, {2}, {3}, {4}}, NewDefaultTree)
+		assert.NoError(t, err)
+		err = ds.setRowSlice(tc.x, tc.y, tc.newRow)
+
+		if tc.wantErr {
+			assert.Error(t, err)
+			return
+		} else {
+			assert.NoError(t, err)
+			assert.Equal(t, tc.want, ds.Flattened())
+		}
+	}
+}
+
+func Test_setColSlice(t *testing.T) {
+	type testCase struct {
+		name    string
+		newCol  [][]byte
+		x       uint
+		y       uint
+		want    [][]byte
+		wantErr bool
+	}
+	testCases := []testCase{
+		{
+			name:    "overwrite the first col",
+			newCol:  [][]byte{{5}, {6}},
+			x:       0,
+			y:       0,
+			want:    [][]byte{{5}, {2}, {6}, {4}},
+			wantErr: false,
+		},
+		{
+			name:    "overwrite the last col",
+			newCol:  [][]byte{{5}, {6}},
+			x:       0,
+			y:       1,
+			want:    [][]byte{{1}, {5}, {3}, {6}},
+			wantErr: false,
+		},
+		{
+			name:    "returns an error if the new col has an invalid chunk size",
+			newCol:  [][]byte{{5, 6}},
+			x:       0,
+			y:       0,
+			wantErr: true,
+		},
+		{
+			name:    "returns an error if the new col would surpass the data square's width",
+			newCol:  [][]byte{{5}, {6}},
+			x:       1,
+			y:       0,
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		ds, err := newDataSquare([][]byte{{1}, {2}, {3}, {4}}, NewDefaultTree)
+		assert.NoError(t, err)
+		err = ds.setColSlice(tc.x, tc.y, tc.newCol)
+
+		if tc.wantErr {
+			assert.Error(t, err)
+			return
+		} else {
+			assert.NoError(t, err)
+			assert.Equal(t, tc.want, ds.Flattened())
+		}
+	}
+}
+
 func BenchmarkEDSRoots(b *testing.B) {
 	for i := 32; i < 513; i *= 2 {
 		square, err := newDataSquare(genRandDS(i*2), NewDefaultTree)