diff --git a/src/OpenFOAM/db/IOstreams/hashes/OSHA1stream.H b/src/OpenFOAM/db/IOstreams/hashes/OSHA1stream.H
index 763745aa25..28c84a64b3 100644
--- a/src/OpenFOAM/db/IOstreams/hashes/OSHA1stream.H
+++ b/src/OpenFOAM/db/IOstreams/hashes/OSHA1stream.H
@@ -32,8 +32,8 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef OSHA1stream_H
-#define OSHA1stream_H
+#ifndef Foam_OSHA1stream_H
+#define Foam_OSHA1stream_H
 
 #include "OSstream.H"
 #include "SHA1.H"
@@ -63,10 +63,17 @@ class osha1stream
 
     protected:
 
+        //- Handle overflow
+        virtual int overflow(int c = EOF)
+        {
+            if (c != EOF) sha1_.append(c);
+            return c;
+        }
+
         //- Put sequence of characters
         virtual std::streamsize xsputn(const char* s, std::streamsize n)
         {
-            sha1_.append(s, n);
+            if (n) sha1_.append(s, n);
             return n;
         }
 
diff --git a/src/OpenFOAM/primitives/hashes/SHA1/SHA1.H b/src/OpenFOAM/primitives/hashes/SHA1/SHA1.H
index 9d9e617a48..54a506034e 100644
--- a/src/OpenFOAM/primitives/hashes/SHA1/SHA1.H
+++ b/src/OpenFOAM/primitives/hashes/SHA1/SHA1.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -42,8 +42,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef SHA1_H
-#define SHA1_H
+#ifndef Foam_SHA1_H
+#define Foam_SHA1_H
 
 #include <string>
 #include <cstdint>
@@ -113,6 +113,9 @@ public:
         //- Reset the hashed data before appending more
         void clear() noexcept;
 
+        //- Append single character
+        inline void append(char c);
+
         //- Append data for processing
         inline SHA1& append(const char* str);
 
diff --git a/src/OpenFOAM/primitives/hashes/SHA1/SHA1I.H b/src/OpenFOAM/primitives/hashes/SHA1/SHA1I.H
index b04b3b6161..beaa3e40f1 100644
--- a/src/OpenFOAM/primitives/hashes/SHA1/SHA1I.H
+++ b/src/OpenFOAM/primitives/hashes/SHA1/SHA1I.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011 OpenFOAM Foundation
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -52,6 +52,12 @@ inline Foam::SHA1::SHA1(const std::string& str)
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
+inline void Foam::SHA1::append(char c)
+{
+    processBytes(&c, 1);
+}
+
+
 inline Foam::SHA1& Foam::SHA1::append(const char* data, size_t len)
 {
     processBytes(data, len);