diff --git a/src/Serilog.Sinks.Seq/Sinks/Seq/HttpLogShipper.cs b/src/Serilog.Sinks.Seq/Sinks/Seq/HttpLogShipper.cs
index b0e5a52..aa9b7d9 100644
--- a/src/Serilog.Sinks.Seq/Sinks/Seq/HttpLogShipper.cs
+++ b/src/Serilog.Sinks.Seq/Sinks/Seq/HttpLogShipper.cs
@@ -19,7 +19,6 @@
 using System.Linq;
 using System.Net;
 using System.Net.Http;
-using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading;
 using Serilog.Core;
@@ -29,6 +28,10 @@
 using System.Threading.Tasks;
 using System.Collections.Generic;
 
+#if HRESULTS
+using System.Runtime.InteropServices;
+#endif
+
 namespace Serilog.Sinks.Seq
 {
     class HttpLogShipper : IDisposable
@@ -394,6 +397,7 @@ static bool IsUnlockedAtLength(string file, long maxLen)
                     return fileStream.Length <= maxLen;
                 }
             }
+#if HRESULTS
             catch (IOException ex)
             {
                 var errorCode = Marshal.GetHRForException(ex) & ((1 << 16) - 1);
@@ -402,6 +406,12 @@ static bool IsUnlockedAtLength(string file, long maxLen)
                     SelfLog.WriteLine("Unexpected I/O exception while testing locked status of {0}: {1}", file, ex);
                 }
             }
+#else
+            catch (IOException)
+            {
+                // Where no HRESULT is available, assume IOExceptions indicate a locked file
+            }
+#endif
             catch (Exception ex)
             {
                 SelfLog.WriteLine("Unexpected exception while testing locked status of {0}: {1}", file, ex);
diff --git a/src/Serilog.Sinks.Seq/project.json b/src/Serilog.Sinks.Seq/project.json
index b817b7c..3432ceb 100644
--- a/src/Serilog.Sinks.Seq/project.json
+++ b/src/Serilog.Sinks.Seq/project.json
@@ -19,7 +19,7 @@
   "frameworks": {
     "net4.5": {
       "buildOptions": {
-        "define": [ "DURABLE", "WAITABLE_TIMER" ]
+        "define": [ "DURABLE", "WAITABLE_TIMER", "HRESULTS" ]
       },
       "frameworkAssemblies": {
         "System.Net.Http": ""