diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 41236eafc17..46d5423d239 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2010-01-27  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* symtab.h (struct symbol <symtab>): New comment on NULL values.
+
 2010-01-27  Doug Evans  <dje@google.com>
 
 	* breakpoint.c (bpstat_stop_status): Delete useless code.
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 8759732ed45..167dfe82ec3 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -554,7 +554,8 @@ struct symbol
   struct type *type;
 
   /* The symbol table containing this symbol.  This is the file
-     associated with LINE.  */
+     associated with LINE.  It can be NULL during symbols read-in but it is
+     never NULL during normal operation.  */
   struct symtab *symtab;
 
   /* Domain code.  */