diff --git a/g10/main.h b/g10/main.h
index 7f3752aac..06cbfc8d8 100644
--- a/g10/main.h
+++ b/g10/main.h
@@ -110,7 +110,7 @@ void unregister_secured_file (const char *fname);
 int  is_secured_file (int fd);
 int  is_secured_filename (const char *fname);
 u16 checksum_u16( unsigned n );
-u16 checksum( byte *p, unsigned n );
+u16 checksum( const byte *p, unsigned n );
 u16 checksum_mpi( gcry_mpi_t a );
 u32 buffer_to_u32( const byte *buffer );
 const byte *get_session_marker( size_t *rlen );
diff --git a/g10/misc.c b/g10/misc.c
index 0d457365b..67a2f1928 100644
--- a/g10/misc.c
+++ b/g10/misc.c
@@ -241,7 +241,7 @@ checksum_u16( unsigned n )
 
 
 u16
-checksum( byte *p, unsigned n )
+checksum (const byte *p, unsigned n)
 {
     u16 a;