diff --git a/src/libdeflate_sys/libdeflate.rs b/src/libdeflate_sys/libdeflate.rs
index 23d1e2534ac7..866300426ea3 100644
--- a/src/libdeflate_sys/libdeflate.rs
+++ b/src/libdeflate_sys/libdeflate.rs
@@ -20,8 +20,15 @@ impl Default for Options {
     }
 }
 
+/// Valid `compression_level` range for `libdeflate_alloc_compressor`. Values
+/// outside this range make the allocator return NULL (indistinguishable from OOM),
+/// so callers must range-check first.
+pub const MIN_COMPRESSION_LEVEL: c_int = 0;
+pub const MAX_COMPRESSION_LEVEL: c_int = 12;
+
 unsafe extern "C" {
-    // Allocation: scalar arg, no preconditions; returns null on OOM.
+    // Allocation: scalar arg, no preconditions; returns null on OOM or
+    // compression_level outside MIN..=MAX_COMPRESSION_LEVEL.
     pub(crate) safe fn libdeflate_alloc_compressor(compression_level: c_int) -> *mut Compressor;
     // NOT safe: `Options` carries caller-supplied `malloc_func`/`free_func`
     // callbacks that libdeflate will invoke and write through. A bogus callback
@@ -254,7 +261,8 @@ impl Compressor {
 pub struct OwnedCompressor(NonNull<Compressor>);
 
 impl OwnedCompressor {
-    /// Allocate a compressor at `level` (0..=12). Returns `None` on OOM.
+    /// Allocate a compressor at `level` ([`MIN_COMPRESSION_LEVEL`]..=[`MAX_COMPRESSION_LEVEL`]).
+    /// Returns `None` on OOM or if `level` is out of range.
     #[inline]
     pub fn new(level: c_int) -> Option<Self> {
         NonNull::new(Compressor::alloc(level)).map(Self)
diff --git a/src/runtime/api/BunObject.rs b/src/runtime/api/BunObject.rs
index 2547980b2d02..c592c826915e 100644
--- a/src/runtime/api/BunObject.rs
+++ b/src/runtime/api/BunObject.rs
@@ -2708,8 +2708,17 @@ pub mod JSZlib {
                 leak_list_into_uint8array(global_this, list)
             }
             Library::Libdeflate => {
-                let Some(mut compressor) = bun_libdeflate::OwnedCompressor::new(level.unwrap_or(6))
-                else {
+                let level = level.unwrap_or(6);
+                if !(bun_libdeflate::MIN_COMPRESSION_LEVEL..=bun_libdeflate::MAX_COMPRESSION_LEVEL)
+                    .contains(&level)
+                {
+                    return Err(global_this.throw_invalid_arguments(format_args!(
+                        "Compression level must be between {} and {} for libdeflate",
+                        bun_libdeflate::MIN_COMPRESSION_LEVEL,
+                        bun_libdeflate::MAX_COMPRESSION_LEVEL,
+                    )));
+                }
+                let Some(mut compressor) = bun_libdeflate::OwnedCompressor::new(level) else {
                     return Err(global_this.throw_out_of_memory());
                 };
                 let encoding = if is_gzip {
diff --git a/test/js/node/zlib/zlib.test.js b/test/js/node/zlib/zlib.test.js
index 164b531e51a3..1167a38455b3 100644
--- a/test/js/node/zlib/zlib.test.js
+++ b/test/js/node/zlib/zlib.test.js
@@ -105,6 +105,36 @@ describe("zlib", () => {
     const data = new TextEncoder().encode("Hello World!".repeat(1));
     expect(() => gunzipSync(data, { library: "zlib" })).toThrow(new Error("incorrect header check"));
   });
+
+  describe("libdeflate level validation", () => {
+    const data = Buffer.alloc(64, "a");
+    // libdeflate_alloc_compressor returns NULL for level outside [0, 12]; that NULL must
+    // surface as an invalid-argument error, not "Out of memory".
+    for (const fn of [gzipSync, deflateSync]) {
+      it(`${fn.name}: out-of-range level throws an argument error, not OOM`, () => {
+        for (const level of [-2, -1, 13, 100]) {
+          let err;
+          try {
+            fn(data, { library: "libdeflate", level });
+          } catch (e) {
+            err = e;
+          }
+          expect(err).toBeDefined();
+          expect(err.message).not.toContain("memory");
+          expect(err.message).toContain("Compression level must be between 0 and 12");
+        }
+      });
+
+      it(`${fn.name}: in-range levels 0..12 succeed and round-trip`, () => {
+        const decompress = fn === gzipSync ? gunzipSync : inflateSync;
+        for (const level of [0, 1, 6, 9, 12]) {
+          const out = fn(data, { library: "libdeflate", level });
+          expect(out.length).toBeGreaterThan(0);
+          expect(Buffer.from(decompress(out, { library: "libdeflate" }))).toEqual(data);
+        }
+      });
+    }
+  });
 });
 
 function* window(buffer, size, advance = size) {