diff --git a/src/libraries/System.Diagnostics.Process/src/Microsoft/Win32/SafeHandles/SafeProcessHandle.Unix.cs b/src/libraries/System.Diagnostics.Process/src/Microsoft/Win32/SafeHandles/SafeProcessHandle.Unix.cs
index 580c921aa243ec..75006648eee457 100644
--- a/src/libraries/System.Diagnostics.Process/src/Microsoft/Win32/SafeHandles/SafeProcessHandle.Unix.cs
+++ b/src/libraries/System.Diagnostics.Process/src/Microsoft/Win32/SafeHandles/SafeProcessHandle.Unix.cs
@@ -270,7 +270,7 @@ private static SafeProcessHandle StartWithShellExecute(ProcessStartInfo startInf
             }
 
             // use default program to open file/url
-            filename = Process.GetPathToOpenFile();
+            filename = Process.GetPathToOpenFile() ?? throw new Win32Exception(Interop.Errors.ERROR_NO_ASSOCIATION);
             string[] openFileArgv = ProcessUtils.ParseArgv(startInfo, filename, ignoreArguments: true);
 
             SafeProcessHandle result = ForkAndExecProcess(