diff --git a/src/earthkit/data/data/wrappers/string.py b/src/earthkit/data/data/wrappers/string.py
index a0763bc37..132e0a3f2 100644
--- a/src/earthkit/data/data/wrappers/string.py
+++ b/src/earthkit/data/data/wrappers/string.py
@@ -53,10 +53,10 @@ def _repr_html_(self):
         return self.describe()._repr_html_()
 
     def bounding_box(self):
-        if "/" in self.data:
-            return tuple(float(x) for x in self.data.split("/"))
+        if "/" in self._data:
+            return tuple(float(x) for x in self._data.split("/"))
         else:
-            raise ValueError(f"Invalid bounding box '{self.data}'")
+            raise ValueError(f"Invalid bounding box '{self._data}'")
 
     def _datetime(self):
         return parse_date(self._data)
diff --git a/tests/sources/test_mars.py b/tests/sources/test_mars.py
index 2e79dda53..469d4b1a7 100644
--- a/tests/sources/test_mars.py
+++ b/tests/sources/test_mars.py
@@ -244,6 +244,22 @@ def test_mars_grib_save():
         assert len(ds1) == 1
 
 
+# @pytest.mark.long_test
+# @pytest.mark.download
+@pytest.mark.skipif(NO_MARS, reason="No access to MARS")
+def test_mars_grib_area_str():
+    s = from_source(
+        "mars",
+        param=["2t"],
+        levtype="sfc",
+        area="50/-50/20/50",
+        grid=[10, 10],
+        prompt=False,
+        date="2023-05-10",
+    ).to_fieldlist()
+    assert len(s) == 1
+
+
 if __name__ == "__main__":
     from earthkit.data.utils.testing import main
 
diff --git a/tests/wrappers/test_string_wrapper.py b/tests/wrappers/test_string_wrapper.py
index 162f8565e..07e430af6 100644
--- a/tests/wrappers/test_string_wrapper.py
+++ b/tests/wrappers/test_string_wrapper.py
@@ -68,3 +68,12 @@ def test_string_wrapper_datetime_list_by(date_format):
     assert ds.to_value() == datetime_list_string + "/by/2"
     assert ds.to_string() == datetime_list_string + "/by/2"
     assert ds.to_datetime_list() == dt
+
+
+def test_string_wrapper_bbox():
+    v = "89/0/-89/360"
+    ds = from_object(v)
+    assert ds._TYPE_NAME == "str"
+    assert "bounding_box" in ds.available_types
+
+    assert ds.bounding_box() == (89.0, 0.0, -89.0, 360.0)