diff --git a/src/Tasks.UnitTests/Exec_Tests.cs b/src/Tasks.UnitTests/Exec_Tests.cs
index 736f1aaf598..3bc0657cab2 100644
--- a/src/Tasks.UnitTests/Exec_Tests.cs
+++ b/src/Tasks.UnitTests/Exec_Tests.cs
@@ -122,7 +122,6 @@ public void Timeout()
         [Fact]
         public void TimeoutFailsEvenWhenExitCodeIsIgnored()
         {
-
             Exec exec = PrepareExec(NativeMethodsShared.IsWindows ? ":foo \n goto foo" : "while true; do sleep 1; done");
             exec.Timeout = 5;
             exec.IgnoreExitCode = true;
@@ -136,8 +135,16 @@ public void TimeoutFailsEvenWhenExitCodeIsIgnored()
             // ToolTask does not log an error on timeout.
             mockEngine.Errors.ShouldBe(0);
 
-            // On non-Windows the exit code of a killed process is 128 + SIGKILL = 137
-            exec.ExitCode.ShouldBe(NativeMethodsShared.IsWindows ? -1 : 137);
+            if (NativeMethodsShared.IsMono)
+            {
+                const int STILL_ACTIVE = 259; // When Process.WaitForExit times out.
+                exec.ExitCode.ShouldBeOneOf(137, STILL_ACTIVE);
+            }
+            else
+            {
+                // On non-Windows the exit code of a killed process is 128 + SIGKILL = 137
+                exec.ExitCode.ShouldBe(NativeMethodsShared.IsWindows ? -1 : 137);
+            }
         }
 
         [Fact]