diff --git a/mysql-test/r/ctype_recoding.result b/mysql-test/r/ctype_recoding.result
index 1c75988fd21..0b5c6f8974c 100644
--- a/mysql-test/r/ctype_recoding.result
+++ b/mysql-test/r/ctype_recoding.result
@@ -181,11 +181,18 @@ select * from t1 where a=_koi8r'
 a
 вася
 select * from t1 where a=concat(_koi8r'вася');
-ERROR HY000: Illegal mix of collations (cp1251_general_ci,IMPLICIT) and (koi8r_general_ci,COERCIBLE) for operation '='
+a
+вася
 select * from t1 where a=_latin1'вася';
 ERROR HY000: Illegal mix of collations (cp1251_general_ci,IMPLICIT) and (latin1_swedish_ci,COERCIBLE) for operation '='
 drop table t1;
 set names latin1;
+create table t1 (a char(10) character set utf8 collate utf8_bin);
+insert into t1 values ('       xxx');
+select * from t1 where a=lpad('xxx',10,' ');
+a
+       xxx
+drop table t1;
 set names koi8r;
 create table t1 (c1 char(10) character set cp1251);
 insert into t1 values ('ъ');
diff --git a/mysql-test/t/ctype_recoding.test b/mysql-test/t/ctype_recoding.test
index 9949ef88da4..5648cea7fd3 100644
--- a/mysql-test/t/ctype_recoding.test
+++ b/mysql-test/t/ctype_recoding.test
@@ -144,8 +144,7 @@ create table t1 (a char(10) character set cp1251);
 insert into t1 values (_koi8r'вася');
 # this is possible:
 select * from t1 where a=_koi8r'вася';
-# this is not possible, because we have a function, not just a constant:
---error 1267
+# this is possible, because we have a function with constant arguments:
 select * from t1 where a=concat(_koi8r'вася');
 # this is not posible, cannot convert _latin1'вася' into cp1251:
 --error 1267
@@ -153,6 +152,14 @@ select * from t1 where a=_latin1'
 drop table t1;
 set names latin1;
 
+#
+# Bug#10446 Illegal mix of collations
+#
+create table t1 (a char(10) character set utf8 collate utf8_bin);
+insert into t1 values ('       xxx');
+select * from t1 where a=lpad('xxx',10,' ');
+drop table t1;
+
 #
 # Check more automatic conversion
 #
diff --git a/sql/item.cc b/sql/item.cc
index 6ca2627dbff..60fa53bf798 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -211,16 +211,8 @@ bool Item::eq(const Item *item, bool binary_cmp) const
 
 Item *Item::safe_charset_converter(CHARSET_INFO *tocs)
 {
-  /*
-    Allow conversion from and to "binary".
-    Don't allow automatic conversion to non-Unicode charsets,
-    as it potentially loses data.
-  */
-  if (collation.collation != &my_charset_bin &&
-      tocs != &my_charset_bin &&
-      !(tocs->state & MY_CS_UNICODE))
-    return NULL; // safe conversion is not possible
-  return new Item_func_conv_charset(this, tocs);
+  Item_func_conv_charset *conv= new Item_func_conv_charset(this, tocs, 1);
+  return conv->safe ? conv : NULL;
 }
 
 
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 6ca6ce62c54..60cb3348590 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -2252,6 +2252,8 @@ String *Item_func_conv::val_str(String *str)
 String *Item_func_conv_charset::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);
+  if (use_cached_value)
+    return null_value ? 0 : &str_value;
   String *arg= args[0]->val_str(str);
   uint dummy_errors;
   if (!arg)
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index 87aee9ac25c..c4505fce248 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -614,10 +614,40 @@ public:
 
 class Item_func_conv_charset :public Item_str_func
 {
+  bool use_cached_value;
 public:
+  bool safe;
   CHARSET_INFO *conv_charset; // keep it public
-  Item_func_conv_charset(Item *a, CHARSET_INFO *cs) :Item_str_func(a)
-  { conv_charset=cs; }
+  Item_func_conv_charset(Item *a, CHARSET_INFO *cs) :Item_str_func(a) 
+  { conv_charset= cs; use_cached_value= 0; safe= 0; }
+  Item_func_conv_charset(Item *a, CHARSET_INFO *cs, bool cache_if_const) 
+    :Item_str_func(a) 
+  {
+    DBUG_ASSERT(args[0]->fixed);
+    conv_charset= cs;
+    if (cache_if_const && args[0]->const_item())
+    {
+      uint errors= 0;
+      String tmp, *str= args[0]->val_str(&tmp);
+      if (!str || str_value.copy(str->ptr(), str->length(),
+                                 str->charset(), conv_charset, &errors))
+        null_value= 1;
+      use_cached_value= 1;
+      safe= (errors == 0);
+    }
+    else
+    {
+      use_cached_value= 0;
+      /*
+        Conversion from and to "binary" is safe.
+        Conversion to Unicode is safe.
+        Other kind of conversions are potentially lossy.
+      */
+      safe= (args[0]->collation.collation == &my_charset_bin ||
+             cs == &my_charset_bin ||
+             (cs->state & MY_CS_UNICODE));
+    }
+  }
   String *val_str(String *);
   void fix_length_and_dec();
   const char *func_name() const { return "convert"; }