diff --git a/src/BizHawk.Client.Common/rewind/ZeldaWinder.cs b/src/BizHawk.Client.Common/rewind/ZeldaWinder.cs
index ebe35d80b8..80d86fe565 100644
--- a/src/BizHawk.Client.Common/rewind/ZeldaWinder.cs
+++ b/src/BizHawk.Client.Common/rewind/ZeldaWinder.cs
@@ -290,7 +290,11 @@ namespace BizHawk.Client.Common
 					_dest = replacement;
 				}
 			}
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER
+			public override void Write(ReadOnlySpan<byte> buffer)
+#else
 			public void Write(ReadOnlySpan<byte> buffer)
+#endif
 			{
 				var requestedSize = _position + buffer.Length;
 				MaybeResize(requestedSize);
@@ -304,7 +308,11 @@ namespace BizHawk.Client.Common
 				_dest[_position] = value;
 				_position = requestedSize;
 			}
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER
+			public override int Read(Span<byte> buffer) => throw new IOException();
+#else
 			public int Read(Span<byte> buffer) => throw new IOException();
+#endif
 		}
 	}
 }
diff --git a/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs b/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs
index 5843b8e3c2..97214aa761 100644
--- a/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs
+++ b/src/BizHawk.Client.Common/rewind/ZwinderBuffer.cs
@@ -443,14 +443,22 @@ namespace BizHawk.Client.Common
 			public override int Read(byte[] buffer, int offset, int count) => throw new IOException();
 			public override long Seek(long offset, SeekOrigin origin) => throw new IOException();
 			public override void SetLength(long value) => throw new IOException();
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER
+			public override int Read(Span<byte> buffer) => throw new IOException();
+#else
 			public int Read(Span<byte> buffer) => throw new IOException();
+#endif
 
 			public override void Write(byte[] buffer, int offset, int count)
 			{
 				Write(new ReadOnlySpan<byte>(buffer, offset, count));
 			}
 
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER
+			public override void Write(ReadOnlySpan<byte> buffer)
+#else
 			public void Write(ReadOnlySpan<byte> buffer)
+#endif
 			{
 				long requestedSize = _position + buffer.Length;
 				while (requestedSize > _notifySize)
@@ -526,7 +534,11 @@ namespace BizHawk.Client.Common
 				return Read(new Span<byte>(buffer, offset, count));
 			}
 
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER
+			public override int Read(Span<byte> buffer)
+#else
 			public int Read(Span<byte> buffer)
+#endif
 			{
 				long n = Math.Min(_size - _position, buffer.Length);
 				int ret = (int)n;
@@ -577,7 +589,11 @@ namespace BizHawk.Client.Common
 			public override void SetLength(long value) => throw new IOException();
 			public override void Write(byte[] buffer, int offset, int count) => throw new IOException();
 
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER
+			public override void Write(ReadOnlySpan<byte> buffer) => throw new IOException();
+#else
 			public void Write(ReadOnlySpan<byte> buffer) => throw new IOException();
+#endif
 		}
 	}
 }
diff --git a/src/BizHawk.Client.EmuHawk/MainForm.cs b/src/BizHawk.Client.EmuHawk/MainForm.cs
index 1b39d292ba..bea63c12f3 100644
--- a/src/BizHawk.Client.EmuHawk/MainForm.cs
+++ b/src/BizHawk.Client.EmuHawk/MainForm.cs
@@ -4796,7 +4796,11 @@ namespace BizHawk.Client.EmuHawk
 			}
 
 			// Create pipe and start the async connection wait
+#if NET5_0_OR_GREATER
+			_singleInstanceServer = NamedPipeServerStreamAcl.Create(
+#else
 			_singleInstanceServer = new NamedPipeServerStream(
+#endif
 					"pipe-{84125ACB-F570-4458-9748-321F887FE795}",
 					PipeDirection.In,
 					1,
diff --git a/src/BizHawk.Common/Extensions/StringExtensions.cs b/src/BizHawk.Common/Extensions/StringExtensions.cs
index 34a39cb9fe..05b87ecb32 100644
--- a/src/BizHawk.Common/Extensions/StringExtensions.cs
+++ b/src/BizHawk.Common/Extensions/StringExtensions.cs
@@ -17,10 +17,10 @@ namespace BizHawk.Common.StringExtensions
 #if !(NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER)
 		public static bool Contains(this string haystack, char needle)
 			=> haystack.IndexOf(needle) >= 0;
-#endif
 
 		public static bool Contains(this string haystack, string needle, StringComparison comparisonType)
 			=> haystack.IndexOf(needle, comparisonType) != -1;
+#endif
 
 		/// <inheritdoc cref="EqualsIgnoreCase"/>
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]