diff --git a/libzopfli-sharp/Zopfli.cs b/libzopfli-sharp/Zopfli.cs
index 4f43bfb..600846d 100644
--- a/libzopfli-sharp/Zopfli.cs
+++ b/libzopfli-sharp/Zopfli.cs
@@ -53,9 +53,9 @@ public static byte[] compress(byte[] data_in, ZopfliFormat type, ZopfliOptions o
 
                 // Compress the data via native methods
                 if (Environment.Is64BitProcess)
-                    ZopfliCompressor64.ZopfliCompress(ref options, type, data_in, data_in.Length, ref result, ref result_size);
+                    ZopfliCompressor64.ZopfliCompress(options, type, data_in, data_in.Length, ref result, ref result_size);
                 else
-                    ZopfliCompressor32.ZopfliCompress(ref options, type, data_in, data_in.Length, ref result, ref result_size);
+                    ZopfliCompressor32.ZopfliCompress(options, type, data_in, data_in.Length, ref result, ref result_size);
 
                 // Copy data back to managed memory and return
                 return NativeUtilities.GetDataFromUnmanagedMemory(result, (int)result_size);
diff --git a/libzopfli-sharp/ZopfliCompressor.cs b/libzopfli-sharp/ZopfliCompressor.cs
index 52b07f4..de27f7b 100644
--- a/libzopfli-sharp/ZopfliCompressor.cs
+++ b/libzopfli-sharp/ZopfliCompressor.cs
@@ -24,7 +24,7 @@ public class ZopfliCompressor32
         /// <param name="data_out">Pointer to the dynamic output array to which the result is appended</param>
         /// <param name="data_out_size">This is the size of the memory block pointed to by the dynamic output array size</param>
         [DllImport("x86\\zopfli.dll", CallingConvention = CallingConvention.Cdecl)]
-        public static extern void ZopfliCompress(ref ZopfliOptions options, ZopfliFormat output_type, byte[] data, int data_size, ref IntPtr data_out, ref UIntPtr data_out_size);
+        public static extern void ZopfliCompress(ZopfliOptions options, ZopfliFormat output_type, byte[] data, int data_size, ref IntPtr data_out, ref UIntPtr data_out_size);
     }
 
     /// <summary>
@@ -42,6 +42,6 @@ public class ZopfliCompressor64
         /// <param name="data_out">Pointer to the dynamic output array to which the result is appended</param>
         /// <param name="data_out_size">This is the size of the memory block pointed to by the dynamic output array size</param>
         [DllImport("amd64\\zopfli.dll", CallingConvention = CallingConvention.Cdecl)]
-        public static extern void ZopfliCompress(ref ZopfliOptions options, ZopfliFormat output_type, byte[] data, int data_size, ref IntPtr data_out, ref UIntPtr data_out_size);
+        public static extern void ZopfliCompress(ZopfliOptions options, ZopfliFormat output_type, byte[] data, int data_size, ref IntPtr data_out, ref UIntPtr data_out_size);
     }
 }