diff --git a/MD5Context.cs b/MD5Context.cs
index 5862bfd87..985a5a0d3 100644
--- a/MD5Context.cs
+++ b/MD5Context.cs
@@ -74,6 +74,9 @@ public sealed class Md5Context : IChecksum
         _provider.TransformFinalBlock(Array.Empty<byte>(), 0, 0);
         var md5Output = new StringBuilder();
 
+        if(_provider.Hash is null)
+            return null;
+
         foreach(byte h in _provider.Hash)
             md5Output.Append(h.ToString("x2"));
 
diff --git a/SHA1Context.cs b/SHA1Context.cs
index f332b9b7e..ccb360a5e 100644
--- a/SHA1Context.cs
+++ b/SHA1Context.cs
@@ -74,6 +74,9 @@ public sealed class Sha1Context : IChecksum
         _provider.TransformFinalBlock(Array.Empty<byte>(), 0, 0);
         var sha1Output = new StringBuilder();
 
+        if(_provider.Hash is null)
+            return null;
+
         foreach(byte h in _provider.Hash)
             sha1Output.Append(h.ToString("x2"));
 
diff --git a/SHA256Context.cs b/SHA256Context.cs
index 1e7e49d90..be65193e3 100644
--- a/SHA256Context.cs
+++ b/SHA256Context.cs
@@ -74,6 +74,9 @@ public sealed class Sha256Context : IChecksum
         _provider.TransformFinalBlock(Array.Empty<byte>(), 0, 0);
         var sha256Output = new StringBuilder();
 
+        if(_provider.Hash is null)
+            return null;
+
         foreach(byte h in _provider.Hash)
             sha256Output.Append(h.ToString("x2"));
 
diff --git a/SHA384Context.cs b/SHA384Context.cs
index 12e397f77..26601c78b 100644
--- a/SHA384Context.cs
+++ b/SHA384Context.cs
@@ -74,6 +74,9 @@ public sealed class Sha384Context : IChecksum
         _provider.TransformFinalBlock(Array.Empty<byte>(), 0, 0);
         var sha384Output = new StringBuilder();
 
+        if(_provider.Hash is null)
+            return null;
+
         foreach(byte h in _provider.Hash)
             sha384Output.Append(h.ToString("x2"));
 
diff --git a/SHA512Context.cs b/SHA512Context.cs
index 44098225d..8dbe6fa22 100644
--- a/SHA512Context.cs
+++ b/SHA512Context.cs
@@ -74,6 +74,9 @@ public sealed class Sha512Context : IChecksum
         _provider.TransformFinalBlock(Array.Empty<byte>(), 0, 0);
         var sha512Output = new StringBuilder();
 
+        if(_provider.Hash is null)
+            return null;
+
         foreach(byte h in _provider.Hash)
             sha512Output.Append(h.ToString("x2"));