diff --git a/changelog.d/10229-fractional-array-index.md b/changelog.d/10229-fractional-array-index.md
new file mode 100644
index 0000000000..05013c7185
--- /dev/null
+++ b/changelog.d/10229-fractional-array-index.md
@@ -0,0 +1,5 @@
+Fix fractional numeric reads on arrays with erased receiver types, including
+lazy JSON arrays: `rows[0.5]` now looks up the property `"0.5"` instead of
+truncating to element zero. The runtime fallback validates the integer range
+before narrowing, preserving negative, non-finite, and large property keys
+and reads of named properties without changing the compiler's inline tiers.
diff --git a/crates/perry-runtime/src/array/dynamic_numeric_key_tests.rs b/crates/perry-runtime/src/array/dynamic_numeric_key_tests.rs
new file mode 100644
index 0000000000..edf23709eb
--- /dev/null
+++ b/crates/perry-runtime/src/array/dynamic_numeric_key_tests.rs
@@ -0,0 +1,120 @@
+//! #10190: the erased-receiver fallback must preserve the original numeric key.
+
+use super::subclass::js_packed_arraylike_index_get;
+use crate::value::js_dyn_index_get;
+use crate::value::{JSValue, TAG_UNDEFINED};
+
+fn receiver(state: u8) -> f64 {
+    if state == 0 {
+        let mut array = crate::array::js_array_alloc(3);
+        for value in [11.0, 22.0, 33.0] {
+            array = crate::array::js_array_push_f64(array, value);
+        }
+        return crate::value::js_nanbox_pointer(array as i64);
+    }
+    let bytes = b"[11,22,33]";
+    let tape = crate::json_tape::build_tape(bytes).unwrap();
+    let text = crate::string::js_string_from_bytes(bytes.as_ptr(), bytes.len() as u32);
+    let scope = crate::gc::RuntimeHandleScope::new();
+    let array = scope
+        .root_raw_mut_ptr(unsafe { crate::json_tape::alloc_lazy_array(&tape.entries, 0, 3, text) });
+    if state == 2 {
+        unsafe { crate::json_tape::force_materialize_lazy(array.get_raw_mut_ptr()) };
+    }
+    let raw = array.get_raw_const_ptr::<crate::json_tape::LazyArrayHeader>();
+    let header = unsafe { crate::value::addr_class::try_read_gc_header(raw as usize) }.unwrap();
+    assert_eq!(header.obj_type, crate::gc::GC_TYPE_LAZY_ARRAY);
+    assert_eq!(unsafe { !(*raw).materialized.is_null() }, state == 2);
+    crate::value::js_nanbox_pointer(raw as i64)
+}
+
+#[test]
+fn non_element_numeric_keys_do_not_truncate_on_regular_lazy_or_materialized_arrays() {
+    for state in 0..3 {
+        let scope = crate::gc::RuntimeHandleScope::new();
+        let array = scope.root_nanbox_f64(receiver(state));
+        for key in [
+            0.5,
+            -0.5,
+            1.5,
+            -1.0,
+            2_147_483_648.0,
+            4_294_967_295.0,
+            f64::NAN,
+            f64::INFINITY,
+            f64::NEG_INFINITY,
+        ] {
+            assert_eq!(
+                js_dyn_index_get(array.get_nanbox_f64(), key).to_bits(),
+                TAG_UNDEFINED,
+                "state={state}, key={key}"
+            );
+            assert_eq!(
+                js_packed_arraylike_index_get(array.get_nanbox_f64(), key, std::ptr::null_mut())
+                    .to_bits(),
+                TAG_UNDEFINED,
+                "packed state={state}, key={key}"
+            );
+        }
+        for (key, expected) in [
+            (0.0, 11.0),
+            (-0.0, 11.0),
+            (1.0, 22.0),
+            (f64::from_bits(JSValue::int32(2).bits()), 33.0),
+        ] {
+            assert_eq!(js_dyn_index_get(array.get_nanbox_f64(), key), expected);
+            assert_eq!(
+                js_packed_arraylike_index_get(array.get_nanbox_f64(), key, std::ptr::null_mut()),
+                expected
+            );
+        }
+    }
+}
+
+#[test]
+fn numeric_named_properties_remain_readable_through_the_dynamic_fallback() {
+    let scope = crate::gc::RuntimeHandleScope::new();
+    let array = scope.root_nanbox_f64(receiver(0));
+    for (key, name) in [
+        (0.5, "0.5"),
+        (-0.5, "-0.5"),
+        (-1.0, "-1"),
+        (4_294_967_295.0, "4294967295"),
+        (f64::NAN, "NaN"),
+        (f64::INFINITY, "Infinity"),
+        (1e21, "1e+21"),
+    ] {
+        let name = crate::string::js_string_from_bytes(name.as_ptr(), name.len() as u32);
+        let raw = JSValue::from_bits(array.get_nanbox_f64().to_bits())
+            .as_pointer::<crate::array::ArrayHeader>()
+            as *mut crate::array::ArrayHeader;
+        crate::array::js_array_set_string_key(raw, name, 91.0);
+        assert_eq!(
+            js_dyn_index_get(array.get_nanbox_f64(), key),
+            91.0,
+            "key={key}"
+        );
+        assert_eq!(
+            js_packed_arraylike_index_get(array.get_nanbox_f64(), key, std::ptr::null_mut()),
+            91.0,
+            "packed key={key}"
+        );
+    }
+    assert_eq!(js_dyn_index_get(array.get_nanbox_f64(), 0.0), 11.0);
+}
+
+#[test]
+fn boxed_integer_keys_keep_their_object_property_semantics() {
+    let scope = crate::gc::RuntimeHandleScope::new();
+    let object = scope.root_raw_mut_ptr(crate::object::js_object_alloc(0, 0));
+    let key = crate::string::js_string_from_bytes(b"2".as_ptr(), 1);
+    crate::object::js_object_set_field_by_name(object.get_raw_mut_ptr(), key, 42.0);
+    let read = |key| {
+        let receiver = crate::value::js_nanbox_pointer(
+            object.get_raw_const_ptr::<crate::object::ObjectHeader>() as i64,
+        );
+        js_dyn_index_get(receiver, key)
+    };
+    assert_eq!(read(2.0), 42.0);
+    assert_eq!(read(f64::from_bits(JSValue::int32(2).bits())), 42.0);
+}
diff --git a/crates/perry-runtime/src/array/mod.rs b/crates/perry-runtime/src/array/mod.rs
index fc2c981e47..76539179fa 100644
--- a/crates/perry-runtime/src/array/mod.rs
+++ b/crates/perry-runtime/src/array/mod.rs
@@ -56,6 +56,8 @@ mod collection_tag_tests;
 #[cfg(test)]
 mod dense_move_tests;
 #[cfg(test)]
+mod dynamic_numeric_key_tests;
+#[cfg(test)]
 mod forwarding_tests;
 #[cfg(test)]
 mod index_get_exit_tests;
diff --git a/crates/perry-runtime/src/value/dyn_index.rs b/crates/perry-runtime/src/value/dyn_index.rs
index 7d267faa82..495f96232b 100644
--- a/crates/perry-runtime/src/value/dyn_index.rs
+++ b/crates/perry-runtime/src/value/dyn_index.rs
@@ -408,13 +408,14 @@ pub extern "C" fn js_dyn_index_get(value: f64, index: f64) -> f64 {
             );
         }
     }
-    // NaN and +/-Infinity are not array indices, but they are still ordinary
-    // property keys (`"NaN"`, `"Infinity"`, `"-Infinity"`) on Objects and
-    // Arrays. Delegate this cold case to the polymorphic key path, which runs
-    // ToPropertyKey and already distinguishes ordinary from integer-indexed
-    // exotic receivers. The old early return made a computed definition such
-    // as `{ [Infinity]: value }` unreadable through `obj[Infinity]`.
-    if index.is_nan() || index.is_infinite() {
+    // The element path below takes an i32, so prove an exact non-negative
+    // index before narrowing. Fractional and negative keys are ordinary
+    // properties: truncating 0.5 (or -0.5) would read element 0 (#10190).
+    // Preserve the original key for ToPropertyKey, including non-finite and
+    // large values; the polymorphic path also handles valid u32 indices
+    // beyond i32::MAX. NaN-boxed INT32 keys retain their existing decoding
+    // in that dispatcher, rather than entering the raw-f64 path below.
+    if !index.is_finite() || index < 0.0 || index > i32::MAX as f64 || index.fract() != 0.0 {
         return crate::object::js_object_get_index_polymorphic(raw_ptr as i64, index);
     }
     let idx_i32 = index as i32;
diff --git a/test-files/test_gap_10190_fractional_array_index.ts b/test-files/test_gap_10190_fractional_array_index.ts
new file mode 100644
index 0000000000..5217c5e31f
--- /dev/null
+++ b/test-files/test_gap_10190_fractional_array_index.ts
@@ -0,0 +1,32 @@
+// #10190: numeric keys that are not array indices are named properties.
+function read(receiver: any, key: any): any { return receiver[key]; }
+function numeric(receiver: any, key: number): any { return receiver[key]; }
+function typed(receiver: number[], key: number): any { return receiver[key]; }
+
+const rows: any = JSON.parse('[{"id":1},{"id":2},{"id":3}]');
+console.log("repro", rows[0.5], rows[-0.5]);
+try {
+  console.log(rows[0.5].id);
+} catch (error) {
+  console.log("repro throws", error instanceof TypeError);
+}
+
+const keys = [0.5, -0.5, 1.5, -1, NaN, Infinity, -Infinity,
+  2147483648, 4294967295, 0, -0, 1, 2, 3];
+for (const array of [[11, 22, 33], JSON.parse('[11,22,33]')]) {
+  for (const key of keys) {
+    console.log("absent", key, read(array, key), numeric(array, key), typed(array, key));
+  }
+  for (let i = 0; i < 9; i++) {
+    const key = keys[i];
+    Object.defineProperty(array, String(key), { value: 100 + i, configurable: true });
+    console.log("own", key, read(array, key), numeric(array, key), typed(array, key));
+  }
+  console.log("elements", array.length, array[0], array[1], array[2]);
+}
+
+const inherited: any = [11, 22];
+const prototype = Object.create(Array.prototype);
+Object.defineProperty(prototype, "0.5", { get() { return this[1] + 7; } });
+Object.setPrototypeOf(inherited, prototype);
+console.log("inherited", read(inherited, 0.5), numeric(inherited, 0.5));