diff --git a/sdk/src/opendecree/_convert.py b/sdk/src/opendecree/_convert.py
index 6cfa126..0b05bda 100644
--- a/sdk/src/opendecree/_convert.py
+++ b/sdk/src/opendecree/_convert.py
@@ -28,13 +28,17 @@ def _parse_timedelta(s: str) -> timedelta:
     """Parse a Go-style duration string (e.g., '24h', '30m', '500ms') to timedelta.
 
     Supported units: h (hours), m (minutes), s (seconds), ms (milliseconds),
-    us/µs (microseconds), ns (nanoseconds). Compound forms like '1h30m' work.
+    us/µs (microseconds), ns (nanoseconds). Compound forms like '1h30m' work,
+    with an optional leading sign applied to the entire duration.
     """
     if not s:
         return timedelta()
 
     total_seconds = 0.0
-    i = 0
+    sign = -1 if s[0] == "-" else 1
+    i = 1 if s[0] in "+-" else 0
+    if i == len(s):
+        raise ValueError(f"invalid duration: {s!r}")
     while i < len(s):
         # Parse number.
         start = i
@@ -66,7 +70,7 @@ def _parse_timedelta(s: str) -> timedelta:
             case _:
                 raise ValueError(f"unknown duration unit: {unit!r} in {s!r}")
 
-    return timedelta(seconds=total_seconds)
+    return timedelta(seconds=sign * total_seconds)
 
 
 def convert_value(raw: str, target_type: type) -> object:
@@ -144,9 +148,11 @@ def typed_value_to_string(tv: object) -> str:
                 if total_s >= 60 and total_s % 60 == 0:
                     return f"{total_s // 60}m"
                 return f"{total_s}s"
-            # Has sub-second component — use float seconds.
-            total_float = total_ns / 1_000_000_000
-            return f"{total_float}s"
+            # Keep fractional seconds in decimal notation that the parser accepts.
+            whole_seconds, nanos = divmod(abs(total_ns), 1_000_000_000)
+            sign = "-" if total_ns < 0 else ""
+            fraction = f"{nanos:09d}".rstrip("0")
+            return f"{sign}{whole_seconds}.{fraction}s"
         case "integer_value" | "number_value" | "string_value" | "url_value" | "json_value":
             return str(val)
         case _:
diff --git a/sdk/tests/test_convert.py b/sdk/tests/test_convert.py
index 58c288d..abda34c 100644
--- a/sdk/tests/test_convert.py
+++ b/sdk/tests/test_convert.py
@@ -71,6 +71,27 @@ def test_convert_timedelta_compound():
     assert convert_value("1h30m", timedelta) == timedelta(hours=1, minutes=30)
 
 
+@pytest.mark.parametrize(
+    ("raw", "expected"),
+    [
+        ("-1s", timedelta(seconds=-1)),
+        ("-1h30m", -timedelta(hours=1, minutes=30)),
+        ("-500ms", timedelta(milliseconds=-500)),
+        ("-1us", timedelta(microseconds=-1)),
+        ("+1h30m", timedelta(hours=1, minutes=30)),
+        ("-0s", timedelta()),
+    ],
+)
+def test_convert_timedelta_signed(raw, expected):
+    assert convert_value(raw, timedelta) == expected
+
+
+@pytest.mark.parametrize("raw", ["+", "-", "1h-30m", "--1s"])
+def test_convert_timedelta_invalid_sign(raw):
+    with pytest.raises(TypeMismatchError, match="cannot convert"):
+        convert_value(raw, timedelta)
+
+
 def test_convert_timedelta_invalid():
     with pytest.raises(TypeMismatchError, match="cannot convert"):
         convert_value("not-a-duration", timedelta)
@@ -277,6 +298,28 @@ def test_typed_value_to_string_duration_fractional():
     assert typed_value_to_string(tv) == "1.5s"
 
 
+@pytest.mark.parametrize(
+    ("seconds", "nanos", "expected", "converted"),
+    [
+        (0, 1, "0.000000001s", timedelta()),
+        (0, 1_000, "0.000001s", timedelta(microseconds=1)),
+        (0, -1_000, "-0.000001s", timedelta(microseconds=-1)),
+        (-1, -500_000_000, "-1.5s", timedelta(seconds=-1.5)),
+        (-60, 0, "-60s", timedelta(minutes=-1)),
+        (86_400, 1_000, "86400.000001s", timedelta(days=1, microseconds=1)),
+    ],
+)
+def test_typed_value_to_string_duration_roundtrip(seconds, nanos, expected, converted):
+    from google.protobuf.duration_pb2 import Duration
+
+    from opendecree._generated.centralconfig.v1 import types_pb2
+
+    tv = types_pb2.TypedValue(duration_value=Duration(seconds=seconds, nanos=nanos))
+    raw = typed_value_to_string(tv)
+    assert raw == expected
+    assert convert_value(raw, timedelta) == converted
+
+
 def test_typed_value_to_string_time():
     from google.protobuf.timestamp_pb2 import Timestamp