diff --git a/changelog.d/9803-module-presized-array-growth.md b/changelog.d/9803-module-presized-array-growth.md
new file mode 100644
index 0000000000..d46375cf34
--- /dev/null
+++ b/changelog.d/9803-module-presized-array-growth.md
@@ -0,0 +1 @@
+Fix out-of-bounds numeric array accesses when a static `new Array(n)` length exceeds the runtime’s dense allocation limit. Large module-level fills now use the guarded storage-growth path.
diff --git a/crates/perry-codegen/src/collectors/ptr_numarray.rs b/crates/perry-codegen/src/collectors/ptr_numarray.rs
index d00e795a5f..fcff52edc5 100644
--- a/crates/perry-codegen/src/collectors/ptr_numarray.rs
+++ b/crates/perry-codegen/src/collectors/ptr_numarray.rs
@@ -8,7 +8,8 @@
 //! as a **numeric-array pointer local** when static analysis proves that for
 //! the local's entire lifetime:
 //!
-//! 1. every element slot in `[0, length)` holds canonical raw-f64 number bits
+//! 1. the initial length fits in the allocated backing store, and every
+//!    element slot in `[0, length)` holds canonical raw-f64 number bits
 //!    or `TAG_HOLE` (never a NaN-boxed pointer/string/bool/undefined), and
 //! 2. `length` never shrinks below the allocation length, and
 //! 3. the binding can never go stale (no growth path exists that fails to
@@ -22,7 +23,8 @@
 //! ## Why it is sound (provenance + containment + density)
 //!
 //! * **Provenance**: the local is initialized by exactly one `Stmt::Let` whose
-//!   init is `new Array(<static n>)` (runtime hole-fills every slot, sets
+//!   init is `new Array(<static n>)` within the runtime's fresh dense limit
+//!   (runtime hole-fills every slot, sets
 //!   `GC_ARRAY_RAW_F64_HOLES`, and stamps the pointer-free GC layout —
 //!   `js_array_constructor_single`) or an EMPTY array literal `[]` (length 0;
 //!   nothing to observe until a numeric push). Density: `new Array(n)` ⇒
@@ -382,6 +384,7 @@ struct UseWalk<'a> {
 impl<'a> UseWalk<'a> {
     /// Resolve a static non-negative array-allocation length: an integer
     /// literal or a module-level `const` recorded in `compile_time_constants`.
+    /// The length must also be backed by dense storage at allocation time.
     fn static_alloc_length(&self, e: &Expr) -> Option<i64> {
         let value = match e {
             Expr::Integer(v) => *v as f64,
@@ -389,7 +392,11 @@ impl<'a> UseWalk<'a> {
             Expr::LocalGet(id) => *self.compile_time_constants.get(id)?,
             _ => return None,
         };
-        if !value.is_finite() || value.fract() != 0.0 || !(0.0..=16_000_000.0).contains(&value) {
+        // #9784: match MAX_FRESH_DENSE_ARRAY_LENGTH in runtime/array/alloc.rs.
+        // Above this limit `new Array(n)` has logical length n but only a
+        // small backing store. A length proof cannot justify an unchecked
+        // slot access there; the guarded tiers must grow/consult storage.
+        if !value.is_finite() || value.fract() != 0.0 || !(0.0..=1_000_000.0).contains(&value) {
             return None;
         }
         Some(value as i64)
@@ -1023,6 +1030,30 @@ mod tests {
         assert_eq!(fact.proven_initial_length, 0);
     }
 
+    #[test]
+    fn fresh_array_proof_requires_allocated_storage_for_the_initial_length() {
+        for (length, should_promote) in [(1_000_000, true), (1_000_001, false)] {
+            assert_eq!(is_promoted(&[alloc_let(length)]), should_promote);
+
+            // Module-level constants take a separate provenance input from
+            // literal lengths; both must respect the runtime allocation cap.
+            let stmts = [let_with(
+                ARR,
+                num_array_ty(),
+                new_array(vec![Expr::LocalGet(OTHER)]),
+            )];
+            let collected = collect_num_array_locals(
+                &stmts,
+                &HashSet::new(),
+                &HashMap::new(),
+                &facts_for(vec![]),
+                &HashMap::from([(OTHER, length as f64)]),
+                &HashSet::new(),
+            );
+            assert_eq!(collected.contains_key(&ARR), should_promote);
+        }
+    }
+
     #[test]
     fn promotes_contained_uses() {
         // Element read, numeric-valued element write (including a read of the
diff --git a/crates/perry/tests/issue_9371_large_presized_array.rs b/crates/perry/tests/issue_9371_large_presized_array.rs
index 8b7dfefeba..bccc0affe1 100644
--- a/crates/perry/tests/issue_9371_large_presized_array.rs
+++ b/crates/perry/tests/issue_9371_large_presized_array.rs
@@ -4,12 +4,34 @@
 //! values or falling into quadratic string-keyed property insertion.
 
 use std::path::PathBuf;
-use std::process::Command;
+use std::process::{Command, Output, Stdio};
+use std::time::{Duration, Instant};
 
 fn perry_bin() -> PathBuf {
     PathBuf::from(env!("CARGO_BIN_EXE_perry"))
 }
 
+fn run_with_timeout(mut command: Command) -> Output {
+    command.stdout(Stdio::piped()).stderr(Stdio::piped());
+    let mut child = command.spawn().expect("run compiled fixture");
+    let deadline = Instant::now() + Duration::from_secs(30);
+    loop {
+        if child.try_wait().expect("poll compiled fixture").is_some() {
+            return child.wait_with_output().expect("collect fixture output");
+        }
+        if Instant::now() >= deadline {
+            child.kill().expect("kill timed out fixture");
+            let output = child.wait_with_output().expect("collect timeout output");
+            panic!(
+                "large array fixture exceeded 30 seconds\nstdout:\n{}\nstderr:\n{}",
+                String::from_utf8_lossy(&output.stdout),
+                String::from_utf8_lossy(&output.stderr)
+            );
+        }
+        std::thread::sleep(Duration::from_millis(25));
+    }
+}
+
 #[test]
 fn large_presized_arrays_fill_densely_and_preserve_every_value() {
     let dir = tempfile::tempdir().expect("tempdir");
@@ -17,7 +39,9 @@ fn large_presized_arrays_fill_densely_and_preserve_every_value() {
     let output = dir.path().join("main_bin");
     std::fs::write(
         &entry,
-        r#"
+        concat!(
+            include_str!("../../../test-files/test_gap_9784_module_presized_array.ts"),
+            r#"
 declare function gc(): void;
 
 function fillAndVerify(slots: number, addExpando: boolean): string {
@@ -51,6 +75,7 @@ huge[16] = 9;
 huge[100000000] = 11;
 console.log(huge.length, huge[0], huge[1] === undefined, huge[16], huge[100000000]);
 "#,
+        ),
     )
     .expect("write fixture");
 
@@ -70,7 +95,11 @@ console.log(huge.length, huge[0], huge[1] === undefined, huge[16], huge[10000000
         String::from_utf8_lossy(&compile.stderr)
     );
 
-    let expected = "900000:0:0.25:899999.25:undefined\n\
+    let expected = "1000000 0 999496507 0 999999\n\
+                    1000001 0 496500 0 1000000\n\
+                    1200000 0 999394967 0 1199999\n\
+                    literal 0 0 1000000\n\
+                    900000:0:0.25:899999.25:undefined\n\
                     1000001:0:0.25:1000000.25:undefined\n\
                     1200000:0:0.25:1199999.25:kept\n\
                     cells 1000001 32640 0 255\n\
@@ -82,7 +111,7 @@ console.log(huge.length, huge[0], huge[1] === undefined, huge[16], huge[10000000
                 .env("PERRY_GC_FORCE_EVACUATE", "1")
                 .env("PERRY_GC_VERIFY_EVACUATION", "1");
         }
-        let run = command.output().expect("run compiled fixture");
+        let run = run_with_timeout(command);
         assert!(
             run.status.success(),
             "compiled fixture failed with moving_gc={moving_gc}\nstatus: {:?}\nstdout:\n{}\nstderr:\n{}",
diff --git a/test-files/test_gap_9784_module_presized_array.ts b/test-files/test_gap_9784_module_presized_array.ts
new file mode 100644
index 0000000000..d77930ecc6
--- /dev/null
+++ b/test-files/test_gap_9784_module_presized_array.ts
@@ -0,0 +1,44 @@
+// #9784: logical array length must not prove backing-store capacity.
+
+const boundarySlots = 1000000;
+const boundary: number[] = new Array(boundarySlots);
+for (let i = 0; i < boundarySlots; i++) boundary[i] = i;
+let boundaryWrong = 0;
+let boundaryChecksum = 0;
+for (let i = 0; i < boundarySlots; i++) {
+  if (boundary[i] !== i) boundaryWrong++;
+  boundaryChecksum = (boundaryChecksum + boundary[i]) % 1000000007;
+}
+console.log(boundarySlots, boundaryWrong, boundaryChecksum, boundary[0], boundary[boundarySlots - 1]);
+
+const aboveSlots = 1000001;
+const above: number[] = new Array(aboveSlots);
+for (let i = 0; i < aboveSlots; i++) above[i] = i;
+let aboveWrong = 0;
+let aboveChecksum = 0;
+for (let i = 0; i < aboveSlots; i++) {
+  if (above[i] !== i) aboveWrong++;
+  aboveChecksum = (aboveChecksum + above[i]) % 1000000007;
+}
+console.log(aboveSlots, aboveWrong, aboveChecksum, above[0], above[aboveSlots - 1]);
+
+const largerSlots = 1200000;
+const larger: number[] = new Array(largerSlots);
+for (let i = 0; i < largerSlots; i++) larger[i] = i;
+let largerWrong = 0;
+let largerChecksum = 0;
+for (let i = 0; i < largerSlots; i++) {
+  if (larger[i] !== i) largerWrong++;
+  largerChecksum = (largerChecksum + larger[i]) % 1000000007;
+}
+console.log(largerSlots, largerWrong, largerChecksum, larger[0], larger[largerSlots - 1]);
+
+// A literal allocation inside a function also supplies a static length proof.
+function literalLocal(): void {
+  const values: number[] = new Array(1000001);
+  for (let i = 0; i < 1000001; i++) values[i] = i;
+  let wrong = 0;
+  for (let i = 0; i < 1000001; i++) if (values[i] !== i) wrong++;
+  console.log("literal", wrong, values[0], values[1000000]);
+}
+literalLocal();