diff --git a/src/instana/tracer.py b/src/instana/tracer.py
index 266f2fd7..0c2c1919 100644
--- a/src/instana/tracer.py
+++ b/src/instana/tracer.py
@@ -29,7 +29,7 @@
 from instana.sampling import InstanaSampler, Sampler
 from instana.span.span import InstanaSpan, get_current_span
 from instana.span_context import SpanContext
-from instana.util.ids import generate_id, hex_id, hex_id_limited
+from instana.util.ids import generate_id, hex_id, internal_id_limited
 
 if TYPE_CHECKING:
     from opentelemetry.trace import Span
@@ -123,15 +123,18 @@ def start_span(
         if parent_context and not isinstance(parent_context, SpanContext):
             if parent_context.is_valid:
                 logger.debug("Converting non-Instana parent context to Instana SpanContext")
-                hex_tid = hex_id(parent_context.trace_id)
+                # OTel trace IDs are 128-bit ints; Instana uses 64-bit internally.
+                # internal_id_limited() masks to the lower 64 bits for trace_id,
+                # while the full 128-bit value is preserved as a hex string in
+                # long_trace_id for W3C traceparent propagation.
                 parent_context = SpanContext(
-                    trace_id=int(hex_id_limited(parent_context.trace_id), 16) if len(hex_tid) > 16 else parent_context.trace_id,
+                    trace_id=internal_id_limited(parent_context.trace_id),
                     span_id=parent_context.span_id,
                     is_remote=parent_context.is_remote,
                     trace_flags=parent_context.trace_flags,
                     trace_state=parent_context.trace_state,
                     trace_parent=None,
-                    long_trace_id=hex_tid if len(hex_tid) > 16 else None,
+                    long_trace_id=hex_id(parent_context.trace_id),
                 )
             else:
                 logger.debug("Non-Instana parent context is invalid, resetting to None")
diff --git a/src/instana/util/ids.py b/src/instana/util/ids.py
index f3fba11b..fa895c9a 100644
--- a/src/instana/util/ids.py
+++ b/src/instana/util/ids.py
@@ -164,10 +164,11 @@ def internal_id(id: Union[int, str]) -> int:
 def internal_id_limited(id: Union[int, str]) -> int:
     """
     Returns a valid id to be used internally. Handles both str and int types.
-    Note: Limits the hex string to 16 chars before conversion.
+    Note: Limits the value to the lower 64 bits.
     """
     if isinstance(id, int):
-        return id
+        # Mask to the lower 64 bits.
+        return id & 0xFFFFFFFFFFFFFFFF
 
     length = len(id)
 
diff --git a/tests/test_tracer.py b/tests/test_tracer.py
index 3c91e42b..68dd6331 100644
--- a/tests/test_tracer.py
+++ b/tests/test_tracer.py
@@ -268,9 +268,10 @@ def test_tracer_kind_propagation_to_readable_span(
 # Parametrized tests: start_span with different context / parent-span types
 # ---------------------------------------------------------------------------
 
-# A valid 128-bit and 64-bit OTel trace_id and span_id
+# A valid 128-bit OTel trace_id; a 64-bit value for Instana-internal use; and a span_id.
+# Note: real OTel trace IDs are always 128-bit per the W3C Trace Context spec.
 _OTEL_128BIT_TRACE_ID = 0x1234567890ABCDEF18BED7B8D2E72F6B
-_OTEL_64BIT_TRACE_ID = 0x18BED7B8D2E72F6B
+_OTEL_64BIT_TRACE_ID = 0x18BED7B8D2E72F6B  # used for Instana SpanContext fixtures only
 _OTEL_SPAN_ID = 0x5FB3484FB90A5BAD
 
 
@@ -326,15 +327,6 @@ def _make_instana_context(trace_id: int, span_id: int) -> Context:
             False,  # NOT a root span – parent_id must be set
             id="otel_span_context_128bit_parent",
         ),
-        # --- OTel SpanContext parent with 64-bit trace ID (valid) ---
-        # The tracer must convert it to an Instana SpanContext and use its trace_id directly.
-        pytest.param(
-            lambda: _make_otel_context(_OTEL_64BIT_TRACE_ID, _OTEL_SPAN_ID, is_valid=True),
-            _OTEL_64BIT_TRACE_ID,
-            None,
-            False,  # NOT a root span – parent_id must be set
-            id="otel_span_context_64bit_parent",
-        ),
         # --- OTel SpanContext parent (invalid, i.e. trace_id=0, span_id=0) ---
         # The tracer must ignore it and create a new root span.
         pytest.param(