diff --git a/pineforge_codegen/codegen/security.py b/pineforge_codegen/codegen/security.py
index 33e82f1..114e5cf 100644
--- a/pineforge_codegen/codegen/security.py
+++ b/pineforge_codegen/codegen/security.py
@@ -2173,6 +2173,19 @@ def _build_security_expr(
             and isinstance(expr_node.callee.object, Identifier)
             and expr_node.callee.object.name == "math"
         ):
+            # A rolling/stateful math reducer (e.g. math.sum -> math::Sum) is
+            # precomputed into a committed _secval_* by the security TA
+            # machinery, exactly like a ta.* call. Return that committed value
+            # instead of falling through to _build_security_math_call, whose
+            # inline lowering only covers scalar math and emits a broken
+            # "unsupported: math.<f>" 0.0 for a reducer. Scalar math
+            # (abs/round/min/max/...) is not a TA site, so this is a no-op.
+            math_site = self._get_ta_site(expr_node)
+            if math_site is not None:
+                math_idx = self._ta_index_by_site_id.get(id(math_site))
+                math_sig = self._security_binding_stack_signature(helper_binding_stack)
+                if math_idx is not None and (math_idx, math_sig) in ta_results:
+                    return ta_results[(math_idx, math_sig)]
             return self._build_security_math_call(
                 sec_id,
                 expr_node.callee.member,
diff --git a/pineforge_codegen/codegen/visit_expr.py b/pineforge_codegen/codegen/visit_expr.py
index 4f6bce6..8f6434c 100644
--- a/pineforge_codegen/codegen/visit_expr.py
+++ b/pineforge_codegen/codegen/visit_expr.py
@@ -373,7 +373,12 @@ def _visit_member_access(self, node: MemberAccess) -> str:
                 if node.member == "position_size":
                     return "signed_position_size()"
                 if node.member == "position_avg_price":
-                    return "position_entry_price_"
+                    # Pine returns `na` when the position is flat
+                    # (position_size == 0); the engine field is 0.0 when flat.
+                    # Guard so the common `na(strategy.position_avg_price)`
+                    # flat/in-position idiom is not silently defeated.
+                    return ("(signed_position_size() == 0.0 ? na<double>() "
+                            ": position_entry_price_)")
                 if node.member == "position_entry_name":
                     return "position_entry_name()"
                 # Trade counts
diff --git a/tests/test_security_math_reducer.py b/tests/test_security_math_reducer.py
new file mode 100644
index 0000000..83ce729
--- /dev/null
+++ b/tests/test_security_math_reducer.py
@@ -0,0 +1,53 @@
+"""Regression: a rolling/stateful math reducer (e.g. ``math.sum``) inside
+``request.security`` must resolve to its committed ``_secval_*`` helper, not the
+scalar-math "unsupported" ``0.0`` fallback.
+
+``request.security(tickerid, "D", math.sum(high[1] - low[1], 10) / 10, ...)``
+precomputes ``math.sum`` as a ``math::Sum`` TA site into ``_secval_N`` (exactly
+like a ``ta.*`` reducer). But ``_build_security_expr`` routed the ``math.*`` node
+to the scalar-math lowering (``_build_security_math_call``, which can only emit
+inline scalar ops) BEFORE the TA-site lookup — so it emitted
+``0.0 /* unsupported: math.sum */`` and the whole security silently returned 0.
+The dispatch must return the committed ``_secval_`` for a math call that is a
+precomputed TA site. Scalar math (abs/round/min/max/...) is not a TA site and
+must still lower inline.
+"""
+
+from __future__ import annotations
+
+import re
+
+from pineforge_codegen import transpile
+
+
+def test_math_sum_in_security_resolves_to_committed_secval():
+    src = """//@version=6
+strategy("t", overlay=true)
+adr = request.security(syminfo.tickerid, "D", math.sum(high[1] - low[1], 10) / 10, lookahead=barmerge.lookahead_off)
+if not na(adr) and adr > 0
+    strategy.entry("L", strategy.long)
+plot(close)
+"""
+    cpp = transpile(src)
+    # The reducer must be precomputed as a rolling math::Sum helper...
+    assert "math::Sum" in cpp
+    # ...and it must NOT degrade to the scalar-math unsupported fallback.
+    assert "/* unsupported: math.sum */" not in cpp
+    # The request.security committed value must reference the _secval_ helper
+    # (here: (_secval_N / 10)), not a literal 0.0.
+    assert re.search(r"_req_sec_\d+\s*=\s*\(_secval_\d+ / 10\)", cpp), cpp
+
+
+def test_scalar_math_in_security_still_lowers_inline():
+    # math.abs is not a TA site: it must keep lowering inline, unaffected by the
+    # reducer fix (guards against over-broadly rerouting all math.* calls).
+    src = """//@version=6
+strategy("t", overlay=true)
+d = request.security(syminfo.tickerid, "D", math.abs(close - open), lookahead=barmerge.lookahead_off)
+if not na(d) and d > 0
+    strategy.entry("L", strategy.long)
+plot(close)
+"""
+    cpp = transpile(src)
+    assert "std::abs" in cpp
+    assert "/* unsupported: math.abs */" not in cpp