diff --git a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisConstraint.cs b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisConstraint.cs
index adeed4e5fc..78c5ea606f 100644
--- a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisConstraint.cs	
+++ b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisConstraint.cs	
@@ -1,9 +1,11 @@
+#nullable enable
+
 namespace BizHawk.Emulation.Common
 {
 	public interface AxisConstraint
 	{
-		public string Class { get; }
+		public string? Class { get; }
 
-		public string PairedAxis { get; }
+		public string? PairedAxis { get; }
 	}
 }
diff --git a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisDict.cs b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisDict.cs
index 88d3577762..e1b2d2633c 100644
--- a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisDict.cs	
+++ b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisDict.cs	
@@ -1,3 +1,5 @@
+#nullable enable
+
 using System.Collections;
 using System.Collections.Generic;
 
diff --git a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisPairOrientation.cs b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisPairOrientation.cs
index 89c5808fcc..4410bb19bc 100644
--- a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisPairOrientation.cs	
+++ b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisPairOrientation.cs	
@@ -1,3 +1,5 @@
+#nullable enable
+
 namespace BizHawk.Emulation.Common
 {
 	/// <summary>represents the direction of <c>(+, +)</c></summary>
diff --git a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisSpec.cs b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisSpec.cs
index 79767e4c11..491a1f3a56 100644
--- a/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisSpec.cs	
+++ b/src/BizHawk.Emulation.Common/Base Implementations/Axes/AxisSpec.cs	
@@ -1,3 +1,5 @@
+#nullable enable
+
 using System;
 
 using BizHawk.Common;
@@ -11,7 +13,7 @@ namespace BizHawk.Emulation.Common
 		/// For instance, a N64 controller's analog range is actually larger than the amount allowed by the plastic that artificially constrains it to lower values
 		/// Axis constraints provide a way to technically allow the full range but have a user option to constrain down to typical values that a real control would have
 		/// </summary>
-		public readonly AxisConstraint Constraint;
+		public readonly AxisConstraint? Constraint;
 
 		public Range<float> FloatRange => ((float) Min).RangeTo(Max);
 
@@ -27,11 +29,11 @@ namespace BizHawk.Emulation.Common
 
 		public int Min => Range.Start;
 
-		public string PairedAxis => Constraint?.PairedAxis;
+		public string? PairedAxis => Constraint?.PairedAxis;
 
 		public readonly Range<int> Range;
 
-		public AxisSpec(Range<int> range, int mid, bool isReversed = false, AxisConstraint constraint = null)
+		public AxisSpec(Range<int> range, int mid, bool isReversed = false, AxisConstraint? constraint = null)
 		{
 			Constraint = constraint;
 			IsReversed = isReversed;
diff --git a/src/BizHawk.Emulation.Common/Base Implementations/Axes/CircularAxisConstraint.cs b/src/BizHawk.Emulation.Common/Base Implementations/Axes/CircularAxisConstraint.cs
index 6d9920093b..1300b9e397 100644
--- a/src/BizHawk.Emulation.Common/Base Implementations/Axes/CircularAxisConstraint.cs	
+++ b/src/BizHawk.Emulation.Common/Base Implementations/Axes/CircularAxisConstraint.cs	
@@ -1,10 +1,12 @@
+#nullable enable
+
 using System;
 
 namespace BizHawk.Emulation.Common
 {
 	public sealed class CircularAxisConstraint : AxisConstraint
 	{
-		public string Class { get; }
+		public string? Class { get; }
 
 		private readonly float Magnitude;
 
diff --git a/src/BizHawk.Emulation.Common/Base Implementations/Axes/NoOpAxisConstraint.cs b/src/BizHawk.Emulation.Common/Base Implementations/Axes/NoOpAxisConstraint.cs
index 5c4b278aea..773d3f6301 100644
--- a/src/BizHawk.Emulation.Common/Base Implementations/Axes/NoOpAxisConstraint.cs	
+++ b/src/BizHawk.Emulation.Common/Base Implementations/Axes/NoOpAxisConstraint.cs	
@@ -1,10 +1,12 @@
+#nullable enable
+
 namespace BizHawk.Emulation.Common
 {
 	public sealed class NoOpAxisConstraint : AxisConstraint
 	{
-		public string Class { get; } = null;
+		public string? Class { get; } = null;
 
-		public string PairedAxis { get; }
+		public string? PairedAxis { get; }
 
 		public NoOpAxisConstraint(string pairedAxis) => PairedAxis = pairedAxis;
 	}