diff --git a/haystack/components/converters/json.py b/haystack/components/converters/json.py
index 9510ed9fcb..300826b196 100644
--- a/haystack/components/converters/json.py
+++ b/haystack/components/converters/json.py
@@ -238,6 +238,9 @@ def _get_content_and_meta(self, source: ByteStream) -> list[tuple[str, dict[str,
                     logger.warning("Expected a scalar value but got {obj}. Skipping it.", obj=obj)
                     continue
 
+                if text is not None and not isinstance(text, str):
+                    text = str(text)
+
                 meta = {}
                 if meta_fields == "*":
                     meta = {k: v for k, v in obj.items() if k != self._content_key}
diff --git a/releasenotes/notes/json-converter-scalar-content-163133a47060a2e7.yaml b/releasenotes/notes/json-converter-scalar-content-163133a47060a2e7.yaml
new file mode 100644
index 0000000000..eaf729f667
--- /dev/null
+++ b/releasenotes/notes/json-converter-scalar-content-163133a47060a2e7.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixed ``JSONConverter`` failing with ``ValueError`` when ``content_key`` contains numeric or boolean scalar values.
+    These values are now converted to strings before creating the ``Document``, while ``null`` values remain unchanged.
diff --git a/test/components/converters/test_json.py b/test/components/converters/test_json.py
index 59fee4875b..c3b5d37f48 100644
--- a/test/components/converters/test_json.py
+++ b/test/components/converters/test_json.py
@@ -511,6 +511,16 @@ def test_run_with_content_key(tmpdir):
     assert result["documents"][2].meta == {}
 
 
+@pytest.mark.parametrize("value, expected", [(123, "123"), (1.5, "1.5"), (True, "True"), (None, None)])
+def test_run_with_content_key_with_scalar_values(value, expected):
+    source = ByteStream.from_string(json.dumps({"body": value}))
+
+    converter = JSONConverter(content_key="body")
+    result = converter.run(sources=[source])
+
+    assert result["documents"][0].content == expected
+
+
 def test_run_with_content_key_and_extra_meta_fields(tmpdir):
     first_test_file = Path(tmpdir / "first_test_file.json")
     second_test_file = Path(tmpdir / "second_test_file.json")