diff --git a/changelog.d/11468-sso-buffer-write.md b/changelog.d/11468-sso-buffer-write.md
new file mode 100644
index 0000000000..fcc7cb907a
--- /dev/null
+++ b/changelog.d/11468-sso-buffer-write.md
@@ -0,0 +1 @@
+**fix(runtime): Buffer `write` / `indexOf` accept a short (SSO) string, so parameterised node-postgres queries no longer segfault (#11430).** Since #10762, `String(n)`, `` `${n}` `` and `n.toString()` return small values as SSO strings, whose characters live inline in the NaN-box with no heap header. `buf.write(s)` and the `<encoding>Write` family masked such a value into a `StringHeader` pointer and dereferenced the inline bytes. node-postgres binds every parameter through `buffer.write(String(value), …)`, so any parameterised query crashed in `js_buffer_write_len`: 0 of 20 runs on main, 20 of 20 with this fix, against a live PostgreSQL 16.15. `indexOf` / `lastIndexOf` / `includes` with an SSO needle returned -1; they now materialize the needle first. The new gap test is `test_gap_11430_buffer_write_short_string`.
diff --git a/crates/perry-runtime/src/buffer/cmp.rs b/crates/perry-runtime/src/buffer/cmp.rs
index 24b503d4af..0905e21c63 100644
--- a/crates/perry-runtime/src/buffer/cmp.rs
+++ b/crates/perry-runtime/src/buffer/cmp.rs
@@ -193,6 +193,24 @@ fn buffer_last_index_of_bytes(buf: *const BufferHeader, needle: &[u8], start: i3
     }
 }
 
+/// The needle bytes of an SSO (inline short string) needle under `encoding`,
+/// or `None` when `needle` is not an SSO string.
+fn sso_needle_bytes(needle: f64, encoding: i32) -> Option<Vec<u8>> {
+    if !crate::value::JSValue::from_bits(needle.to_bits()).is_short_string() {
+        return None;
+    }
+    let str_ptr =
+        crate::value::js_get_string_pointer_unified(needle) as usize as *const StringHeader;
+    if str_ptr.is_null() {
+        return None;
+    }
+    let owned = unsafe { crate::string::OwnedStringBytes::copy_from_header(str_ptr) };
+    Some(super::from::buffer_string_bytes_for_encoding(
+        owned.as_bytes(),
+        encoding,
+    ))
+}
+
 fn buffer_search_needle_with_encoding(
     buf: *const BufferHeader,
     needle: f64,
@@ -203,6 +221,11 @@ fn buffer_search_needle_with_encoding(
     }
     let needle_bits = needle.to_bits();
     let top16 = needle_bits >> 48;
+    // #11430: an SSO short string carries its bytes inline (no heap header),
+    // so it must be materialized before the heap-string branch can read it.
+    if let Some(bytes) = sso_needle_bytes(needle, encoding) {
+        return Some(bytes);
+    }
 
     let raw_ptr = if top16 >= 0x7FF8 {
         (needle_bits & 0x0000_FFFF_FFFF_FFFF) as usize
@@ -263,6 +286,9 @@ pub extern "C" fn js_buffer_index_of_enc(
     }
     let needle_bits = needle.to_bits();
     let top16 = needle_bits >> 48;
+    if let Some(bytes) = sso_needle_bytes(needle, encoding) {
+        return buffer_index_of_bytes(buf, &bytes, start);
+    }
 
     // Buffer needle (POINTER_TAG-boxed or raw)
     let raw_ptr = if top16 >= 0x7FF8 {
diff --git a/crates/perry-runtime/src/object/buffer_dispatch.rs b/crates/perry-runtime/src/object/buffer_dispatch.rs
index 84c0ffe3d3..d1b5363125 100644
--- a/crates/perry-runtime/src/object/buffer_dispatch.rs
+++ b/crates/perry-runtime/src/object/buffer_dispatch.rs
@@ -18,6 +18,20 @@ fn is_buffer_dispatch_string(value: f64) -> bool {
     jsval.is_string() || jsval.is_short_string()
 }
 
+/// The `StringHeader` for a string argument `is_buffer_dispatch_string`
+/// accepted. #11430: that predicate admits SSO short strings, whose NaN-box
+/// carries the characters inline — there is no heap header behind the low 48
+/// bits. Masking them into a pointer (what the `write` arms did) dereferenced
+/// the inline bytes as an address. `String(7)` returns SSO since #10762, so
+/// node-postgres' bind of any short numeric parameter
+/// (`writer.addInt32PrefixedString(String(value))` → `buffer.write(...)`)
+/// segfaulted. `js_get_string_pointer_unified` materializes an SSO value onto
+/// the heap and returns a heap string's header unchanged.
+fn buffer_dispatch_string_ptr(value: f64) -> *const crate::string::StringHeader {
+    crate::value::js_get_string_pointer_unified(value) as usize
+        as *const crate::string::StringHeader
+}
+
 fn buffer_dispatch_i32(value: f64) -> i32 {
     let jsval = JSValue::from_bits(value.to_bits());
     if jsval.is_int32() {
@@ -820,13 +834,7 @@ pub unsafe fn dispatch_buffer_method(
                 );
             }
             let enc = fixed_slice_write_encoding(method_name).unwrap_or(0);
-            let str_bits = args[0].to_bits();
-            let str_addr = if (str_bits >> 48) >= 0x7FF8 {
-                str_bits & 0x0000_FFFF_FFFF_FFFF
-            } else {
-                str_bits
-            };
-            let str_ptr = str_addr as *const crate::string::StringHeader;
+            let str_ptr = buffer_dispatch_string_ptr(args[0]);
             let offset = if args.len() >= 2 { arg_i32(1) } else { 0 };
             let max_len = if args.len() >= 3 {
                 arg_i32(2)
@@ -846,13 +854,7 @@ pub unsafe fn dispatch_buffer_method(
                     "ERR_INVALID_ARG_TYPE",
                 );
             }
-            let str_bits = args[0].to_bits();
-            let str_addr = if (str_bits >> 48) >= 0x7FF8 {
-                str_bits & 0x0000_FFFF_FFFF_FFFF
-            } else {
-                str_bits
-            };
-            let str_ptr = str_addr as *const crate::string::StringHeader;
+            let str_ptr = buffer_dispatch_string_ptr(args[0]);
             let (offset, max_len, enc) = buffer_write_args((*buf_ptr).length as i32, &args[1..]);
             crate::buffer::js_buffer_write_len(buf_ptr, str_ptr, offset, max_len, enc) as f64
         }
diff --git a/test-files/test_gap_11430_buffer_write_short_string.ts b/test-files/test_gap_11430_buffer_write_short_string.ts
new file mode 100644
index 0000000000..04d164ec4e
--- /dev/null
+++ b/test-files/test_gap_11430_buffer_write_short_string.ts
@@ -0,0 +1,51 @@
+// #11430: Buffer methods must accept a SHORT string value. Since #10762,
+// `String(n)`, `` `${n}` `` and `n.toString()` return small numbers as SSO
+// (inline short strings): the characters live in the NaN-box itself, with no
+// heap header behind them. `buf.write(s)` and the `<encoding>Write` family
+// masked the value into a pointer anyway and read the inline bytes as an
+// address — a segfault. node-postgres binds every parameter as
+// `writer.addInt32PrefixedString(String(value))` → `buffer.write(...)`, so any
+// parameterised pg query with a short value crashed. `indexOf` /
+// `lastIndexOf` with an SSO needle returned -1.
+const s = String(7);
+const t = String(123456);
+const neg = (-42).toString();
+const tpl = `${3.5}`;
+
+const b = Buffer.alloc(12);
+console.log("write:", b.write(s), b.write(t, 1), b.write(s, 8, 2), b.write(t, 9, 2, "latin1"), b.toString("hex"));
+console.log("write neg/tpl:", Buffer.alloc(6).write(neg, 0, "utf8"), Buffer.alloc(6).write(tpl, 2));
+console.log("utf8Write:", Buffer.alloc(4).utf8Write(s, 1), "latin1Write:", Buffer.alloc(4).latin1Write(t, 0, 2));
+console.log("hexWrite:", Buffer.alloc(4).hexWrite(String(12), 0));
+console.log("indexOf:", Buffer.from("xx7yy7").indexOf(s), Buffer.from("xx7yy7").lastIndexOf(s), Buffer.from("x123456").includes(t));
+console.log("indexOf enc:", Buffer.from("xx7yy").indexOf(s, 0, "latin1"));
+console.log("from/byteLength/fill:", Buffer.from(t).toString("hex"), Buffer.byteLength(s), Buffer.alloc(3).fill(s).toString());
+
+// node-postgres' Writer.addInt32PrefixedString (pg-protocol 1.x), verbatim shape.
+class Writer {
+  buffer = Buffer.allocUnsafe(16);
+  offset = 5;
+  ensure(size: number) {
+    if (this.buffer.length - this.offset < size) {
+      const old = this.buffer;
+      this.buffer = Buffer.allocUnsafe(old.length + (old.length >> 1) + size);
+      old.copy(this.buffer);
+    }
+  }
+  addInt32PrefixedString(value: string) {
+    const len = Buffer.byteLength(value);
+    this.ensure(4 + len);
+    const buffer = this.buffer;
+    let offset = this.offset;
+    buffer[offset++] = (len >>> 24) & 0xff;
+    buffer[offset++] = (len >>> 16) & 0xff;
+    buffer[offset++] = (len >>> 8) & 0xff;
+    buffer[offset++] = len & 0xff;
+    buffer.write(value, offset, "utf-8");
+    this.offset = offset + len;
+    return this;
+  }
+}
+const w = new Writer();
+for (const v of [7, 42, 123456, -1, 0]) w.addInt32PrefixedString(String(v));
+console.log("pg bind:", w.buffer.subarray(5, w.offset).toString("hex"));