diff --git a/src/libraries/System.Diagnostics.Process/tests/ProcessTests.cs b/src/libraries/System.Diagnostics.Process/tests/ProcessTests.cs
index 901cfcfa78a024..be23483549c60d 100644
--- a/src/libraries/System.Diagnostics.Process/tests/ProcessTests.cs
+++ b/src/libraries/System.Diagnostics.Process/tests/ProcessTests.cs
@@ -93,6 +93,10 @@ public static IEnumerable<object[]> SignalTestData()
             {
                 foreach (PosixSignal signal in Enum.GetValues<PosixSignal>())
                 {
+                    if (signal == PosixSignal.SIGKILL)
+                    {
+                        continue; // SIGKILL cannot be caught or ignored
+                    }
                     yield return new object[] { signal };
                 }
                 // Test a few raw signals.
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/PosixSignal.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/PosixSignal.cs
index e1f278fbd6f557..cc047934908651 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/PosixSignal.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/PosixSignal.cs
@@ -42,6 +42,10 @@ public enum PosixSignal
 
         /// <summary>Stop typed at terminal</summary>
         [UnsupportedOSPlatform("windows")]
-        SIGTSTP = -10
+        SIGTSTP = -10,
+
+        /// <summary>Kill (cannot be caught or ignored)</summary>
+        [UnsupportedOSPlatform("windows")]
+        SIGKILL = -11
     }
 }
diff --git a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
index d4923a544cc3a0..07ef66f0e6a62d 100644
--- a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
+++ b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
@@ -1581,6 +1581,8 @@ public OptionalAttribute() { }
     }
     public enum PosixSignal
     {
+        [System.Runtime.Versioning.UnsupportedOSPlatformAttribute("windows")]
+        SIGKILL = -11,
         [System.Runtime.Versioning.UnsupportedOSPlatformAttribute("windows")]
         SIGTSTP = -10,
         [System.Runtime.Versioning.UnsupportedOSPlatformAttribute("windows")]
diff --git a/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/PosixSignalRegistrationTests.Unix.cs b/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/PosixSignalRegistrationTests.Unix.cs
index 9a4b9f37a8b3d0..95c728174adf03 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/PosixSignalRegistrationTests.Unix.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/PosixSignalRegistrationTests.Unix.cs
@@ -16,13 +16,19 @@ public partial class PosixSignalRegistrationTests
     {
         public static IEnumerable<object[]> UninstallableSignals()
         {
+            yield return new object[] { PosixSignal.SIGKILL };
             yield return new object[] { (PosixSignal)9 };
         }
 
         public static IEnumerable<object[]> SupportedSignals()
         {
             foreach (PosixSignal value in Enum.GetValues(typeof(PosixSignal)))
-                yield return new object[] { value };
+            {
+                if (value != PosixSignal.SIGKILL)
+                {
+                    yield return new object[] { value };
+                }
+            }
         }
 
         public static IEnumerable<object[]> UnsupportedSignals()
@@ -252,7 +258,12 @@ public static TheoryData<PosixSignal> PosixSignalAsRawValues
                 var data = new TheoryData<PosixSignal>();
                 foreach (var value in Enum.GetValues(typeof(PosixSignal)))
                 {
-                    int signo = GetPlatformSignalNumber((PosixSignal)value);
+                    PosixSignal signal = (PosixSignal)value;
+                    if (signal == PosixSignal.SIGKILL)
+                    {
+                        continue; // SIGKILL cannot be registered
+                    }
+                    int signo = GetPlatformSignalNumber(signal);
                     Assert.True(signo > 0, "Expected raw signal number to be greater than 0.");
                     data.Add((PosixSignal)signo);
                 }
diff --git a/src/native/libs/System.Native/pal_signal.c b/src/native/libs/System.Native/pal_signal.c
index 352458c8719f08..33be19b7faf37d 100644
--- a/src/native/libs/System.Native/pal_signal.c
+++ b/src/native/libs/System.Native/pal_signal.c
@@ -129,6 +129,10 @@ static bool TryConvertSignalCodeToPosixSignal(int signalCode, PosixSignal* posix
             *posixSignal = PosixSignalSIGTSTP;
             return true;
 
+        case SIGKILL:
+            *posixSignal = PosixSignalSIGKILL;
+            return true;
+
         default:
             *posixSignal = (PosixSignal)signalCode;
             return false;
@@ -169,6 +173,9 @@ int32_t SystemNative_GetPlatformSignalNumber(PosixSignal signal)
         case PosixSignalSIGTSTP:
             return SIGTSTP;
 
+        case PosixSignalSIGKILL:
+            return SIGKILL;
+
         case PosixSignalInvalid:
             break;
     }
diff --git a/src/native/libs/System.Native/pal_signal.h b/src/native/libs/System.Native/pal_signal.h
index c3c21009dc836c..d462b611ccb5de 100644
--- a/src/native/libs/System.Native/pal_signal.h
+++ b/src/native/libs/System.Native/pal_signal.h
@@ -44,7 +44,8 @@ typedef enum
     PosixSignalSIGWINCH = -7,
     PosixSignalSIGTTIN = -8,
     PosixSignalSIGTTOU = -9,
-    PosixSignalSIGTSTP = -10
+    PosixSignalSIGTSTP = -10,
+    PosixSignalSIGKILL = -11
 } PosixSignal;
 
 typedef int32_t (*PosixSignalHandler)(int32_t signalCode, PosixSignal signal);