=== modified file 'sql/sql_priv.h'
--- sql/sql_priv.h	2012-06-12 07:29:56 +0000
+++ sql/sql_priv.h	2012-09-12 07:24:00 +0000
@@ -151,6 +151,11 @@
 */
 #define OPTION_ALLOW_BATCH              (ULL(1) << 36) // THD, intern (slave)
 
+/*
+  Allow ALTER table commands to reset a column's comment when the length > 0
+ */
+#define OPTION_ALLOW_RESET_COMMENT    (ULL(1) << 37) 
+
 /* The rest of the file is included in the server only */
 #ifndef MYSQL_CLIENT
 

=== modified file 'sql/sql_table.cc'
--- sql/sql_table.cc	2012-07-10 14:13:02 +0000
+++ sql/sql_table.cc	2012-09-12 07:24:00 +0000
@@ -5370,6 +5370,12 @@
     }
     if (def)
     {						// Field is changed
+      if (!(thd->variables.option_bits & OPTION_ALLOW_RESET_COMMENT) && field->comment.length && !def->comment.length)
+      {
+        my_error(ER_FPARSER_EOF_IN_COMMENT, MYF(0), def->change);
+        goto err;
+      }
+      
       def->field=field;
       if (!def->after)
       {

=== modified file 'sql/sys_vars.cc'
--- sql/sys_vars.cc	2012-06-12 07:29:56 +0000
+++ sql/sys_vars.cc	2012-09-12 07:24:00 +0000
@@ -2525,6 +2525,12 @@
        REVERSE(OPTION_NO_FOREIGN_KEY_CHECKS),
        DEFAULT(TRUE), NO_MUTEX_GUARD, IN_BINLOG);
 
+static Sys_var_bit Sys_not_allow_reset_comment(
+       "not_allow_reset_comment", "not_allow_reset_comment",
+       SESSION_VAR(option_bits), NO_CMD_LINE,
+       REVERSE(OPTION_ALLOW_RESET_COMMENT),
+       DEFAULT(FALSE), NO_MUTEX_GUARD, IN_BINLOG);
+
 static Sys_var_bit Sys_unique_checks(
        "unique_checks", "unique_checks",
        SESSION_VAR(option_bits), NO_CMD_LINE,