diff --git a/Assets/Example/Example.cs b/Assets/Example/Example.cs
index 310514f..71efede 100644
--- a/Assets/Example/Example.cs
+++ b/Assets/Example/Example.cs
@@ -1,4 +1,3 @@
-#if UNITY_2019_3_OR_NEWER
 using System.Collections.Generic;
 using System;
 using UnityEditor;
@@ -126,6 +125,4 @@ public class AppleDrawer : PropertyDrawer
 		return EditorGUIUtility.singleLineHeight;
 	}
 }
-#endif
-
 #endif
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/AdvancedTypePopup.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/AdvancedTypePopup.cs
index b8bff65..04f769e 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/AdvancedTypePopup.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/AdvancedTypePopup.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System;
+using System;
 using System.Linq;
 using System.Collections.Generic;
 using UnityEngine;
@@ -137,5 +136,4 @@ namespace MackySoft.SerializeReferenceExtensions.Editor {
 		}
 
 	}
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/MackySoft.SerializeReferenceExtensions.Editor.asmdef b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/MackySoft.SerializeReferenceExtensions.Editor.asmdef
index 49a3ce2..c46d84a 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/MackySoft.SerializeReferenceExtensions.Editor.asmdef
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/MackySoft.SerializeReferenceExtensions.Editor.asmdef
@@ -12,9 +12,7 @@
     "overrideReferences": false,
     "precompiledReferences": [],
     "autoReferenced": true,
-    "defineConstraints": [
-        "UNITY_2019_3_OR_NEWER"
-    ],
+    "defineConstraints": [],
     "versionDefines": [],
     "noEngineReferences": false
 }
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs
index 0d84906..646b9f2 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System;
+using System;
 using System.Reflection;
 using UnityEditor;
 using UnityEngine;
@@ -44,5 +43,4 @@ namespace MackySoft.SerializeReferenceExtensions.Editor
 		}
 
 	}
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/PropertyDrawerCache.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/PropertyDrawerCache.cs
index df1bf09..9a1cbe2 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/PropertyDrawerCache.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/PropertyDrawerCache.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System;
+using System;
 using System.Collections.Generic;
 using UnityEditor;
 using System.Reflection;
@@ -78,5 +77,4 @@ namespace MackySoft.SerializeReferenceExtensions.Editor
 		}
 
 	}
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SerializedPropertyExtensions.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SerializedPropertyExtensions.cs
index 135fe25..b26177e 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SerializedPropertyExtensions.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SerializedPropertyExtensions.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System.Collections.Generic;
+using System.Collections.Generic;
 using UnityEditor;
 
 namespace MackySoft.SerializeReferenceExtensions.Editor
@@ -27,5 +26,4 @@ namespace MackySoft.SerializeReferenceExtensions.Editor
 			}
 		}
 	}
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SubclassSelectorDrawer.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SubclassSelectorDrawer.cs
index 6cdbecb..898d199 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SubclassSelectorDrawer.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/SubclassSelectorDrawer.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System;
+using System;
 using System.Linq;
 using System.Collections.Generic;
 using UnityEngine;
@@ -198,5 +197,4 @@ namespace MackySoft.SerializeReferenceExtensions.Editor
 		}
 
 	}
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/TypeMenuUtility.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/TypeMenuUtility.cs
index 3465f19..28d74b3 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/TypeMenuUtility.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/TypeMenuUtility.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System;
+using System;
 using System.Linq;
 using System.Collections.Generic;
 using UnityEditor;
@@ -55,5 +54,4 @@ namespace MackySoft.SerializeReferenceExtensions.Editor {
 		}
 
 	}
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/AddTypeMenuAttribute.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/AddTypeMenuAttribute.cs
index c02c408..9f36c1e 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/AddTypeMenuAttribute.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/AddTypeMenuAttribute.cs
@@ -1,6 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-
-using System;
+using System;
 	
 /// <summary>
 /// An attribute that overrides the name of the type displayed in the SubclassSelector popup.
@@ -34,5 +32,4 @@ public sealed class AddTypeMenuAttribute : Attribute {
 		return (splittedDisplayName.Length != 0) ? splittedDisplayName[splittedDisplayName.Length - 1] : null;
 	}
 
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/HideInTypeMenuAttribute.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/HideInTypeMenuAttribute.cs
index 716aaac..0809014 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/HideInTypeMenuAttribute.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/HideInTypeMenuAttribute.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System;
+using System;
 
 /// <summary>
 /// An attribute that hides the type in the SubclassSelector.
@@ -7,5 +6,4 @@ using System;
 [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Interface, AllowMultiple = false, Inherited = false)]
 public sealed class HideInTypeMenuAttribute : Attribute {
 
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/MackySoft.SerializeReferenceExtensions.asmdef b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/MackySoft.SerializeReferenceExtensions.asmdef
index a5bd920..d4d9e0a 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/MackySoft.SerializeReferenceExtensions.asmdef
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/MackySoft.SerializeReferenceExtensions.asmdef
@@ -8,9 +8,7 @@
     "overrideReferences": false,
     "precompiledReferences": [],
     "autoReferenced": true,
-    "defineConstraints": [
-        "UNITY_2019_3_OR_NEWER"
-    ],
+    "defineConstraints": [],
     "versionDefines": [],
     "noEngineReferences": false
 }
\ No newline at end of file
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/SubclassSelectorAttribute.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/SubclassSelectorAttribute.cs
index e6704c3..8692fe7 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/SubclassSelectorAttribute.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Runtime/SubclassSelectorAttribute.cs
@@ -1,5 +1,4 @@
-#if UNITY_2019_3_OR_NEWER
-using System;
+using System;
 using UnityEngine;
 
 /// <summary>
@@ -8,5 +7,4 @@ using UnityEngine;
 [AttributeUsage(AttributeTargets.Field,AllowMultiple = false)]
 public sealed class SubclassSelectorAttribute : PropertyAttribute {
 	
-}
-#endif
\ No newline at end of file
+}
\ No newline at end of file