diff --git a/Base64/FromBase64Transform.cs b/Base64/FromBase64Transform.cs
index b87f376..a2c4813 100644
--- a/Base64/FromBase64Transform.cs
+++ b/Base64/FromBase64Transform.cs
@@ -83,8 +83,9 @@ public unsafe int TransformBlock(Block block)
                     fixed (char* cp = tempCharBuffer)
                     {
                         nWritten = ASCII.GetChars(startPtr, 4 * numBlocks, cp, bufferSize);
-                    }
-
+                    }
+
+#if NETFRAMEWORK
                     fixed (byte* op = block.outputBuffer)
                     {
                         int outputBytes = UnsafeConvert.FromBase64CharArray(tempCharBuffer, 0, nWritten, op + block.outputOffset);
@@ -92,8 +93,17 @@ public unsafe int TransformBlock(Block block)
                         block.outputOffset += outputBytes;
                         totalOutputBytes += outputBytes;
                     }
-
-                    // If we couldn't write a complete block, try to find 4 bytes starting from the last space.
+#endif
+#if NET5_0_OR_GREATER
+                    if (!Convert.TryFromBase64Chars(tempCharBuffer.AsSpan().Slice(0, nWritten), block.outputBuffer.AsSpan().Slice(block.outputOffset), out int outputBytes))
+                    {
+                        throw new FormatException();
+                    }
+
+                    block.outputOffset += outputBytes;
+                    totalOutputBytes += outputBytes;
+#endif
+                    // If we couldn't write a complete block, try to find 4 bytes starting from the last space.
                     int remainder = effectiveCount % 4;
 
                     if (remainder != 0)
@@ -119,8 +129,9 @@ public unsafe int TransformBlock(Block block)
                             fixed (byte* tp = this.tempByteBuffer)
                             {
                                 nWritten = ASCII.GetChars(tp, 4, cp, bufferSize);
-                            }
-
+                            }
+
+#if NETFRAMEWORK
                             fixed (byte* op = block.outputBuffer)
                             {
                                 int outputBytes = UnsafeConvert.FromBase64CharArray(tempCharBuffer, 0, nWritten, op + block.outputOffset);
@@ -128,6 +139,16 @@ public unsafe int TransformBlock(Block block)
                                 block.outputOffset += outputBytes;
                                 totalOutputBytes += outputBytes;
                             }
+#endif
+#if NET5_0_OR_GREATER
+                            if (!Convert.TryFromBase64Chars(tempCharBuffer.AsSpan().Slice(0, nWritten), block.outputBuffer.AsSpan().Slice(block.outputOffset), out int outputBytes2))
+                            {
+                                throw new FormatException();
+                            }
+
+                            block.outputOffset += outputBytes2;
+                            totalOutputBytes += outputBytes2;
+#endif
 
                             // advance startPtr past the block just written
                             startPtr = tmpPtr;
@@ -223,8 +244,9 @@ private unsafe int FlushTempBuffer(Block block)
                 fixed (byte* tp = this.tempByteBuffer)
                 {
                     nWritten = ASCII.GetChars(tp, 4, cp, bufferSize);
-                }
-
+                }
+
+#if NETFRAMEWORK
                 fixed (byte* op = block.outputBuffer)
                 {
                     int outputBytes = UnsafeConvert.FromBase64CharArray(tempCharBuffer, 0, nWritten, op + block.outputOffset);
@@ -232,6 +254,16 @@ private unsafe int FlushTempBuffer(Block block)
                     block.outputOffset += outputBytes;
                     totalOutputBytes += outputBytes;
                 }
+#endif
+#if NET5_0_OR_GREATER
+                if (!Convert.TryFromBase64Chars(tempCharBuffer.AsSpan().Slice(0, nWritten), block.outputBuffer.AsSpan().Slice(block.outputOffset), out int outputBytes2))
+                {
+                    throw new FormatException();
+                }
+
+                block.outputOffset += outputBytes2;
+                totalOutputBytes += outputBytes2;
+#endif
 
                 // advance offset
                 int count = (int)(startPtr - (byte*)(inputPtr + block.inputOffset));
diff --git a/Base64/UnsafeConvert.cs b/Base64/UnsafeConvert.cs
index d398dd2..50759b8 100644
--- a/Base64/UnsafeConvert.cs
+++ b/Base64/UnsafeConvert.cs
@@ -6,7 +6,8 @@
 using System.Text;
 
 namespace Base64
-{
+{
+#if NETFRAMEWORK
     public static class UnsafeConvert
     {
         /// <summary>
@@ -59,12 +60,12 @@ private static unsafe int FromBase64CharPtr(char* inputPtr, int inputLength, byt
             // Note that actualResultLength can differ from resultLength if the caller is modifying the array
             // as it is being converted. Silently ignore the failure.
             // Consider throwing exception in an non in-place release.
-        }
-
-        private static readonly MethodInfo FromBase64_DecodeMethodInfo = typeof(Convert).GetMethod("FromBase64_Decode", BindingFlags.Static | BindingFlags.NonPublic);
+        }
 
-        // no measurable overhead from reflection here - it's not in a tight loop.
-        // Can we turn this into a func to avoid allocating the args array? Pointers still need to be boxed.
+        private static readonly MethodInfo FromBase64_DecodeMethodInfo = typeof(Convert).GetMethod("FromBase64_Decode", BindingFlags.Static | BindingFlags.NonPublic);
+
+        // no measurable overhead from reflection here - it's not in a tight loop.
+        // Can we turn this into a func to avoid allocating the args array? Pointers still need to be boxed.
         public static unsafe int FromBase64_DecodeReflect(
           char* startInputPtr,
           int inputLength,
@@ -87,4 +88,5 @@ public static unsafe int FromBase64_DecodeReflect(
             }
         }
     }
+#endif
 }