diff --git a/mysql-test/r/update.result b/mysql-test/r/update.result
index 4a9e95fb89e..d83952e118b 100644
--- a/mysql-test/r/update.result
+++ b/mysql-test/r/update.result
@@ -226,3 +226,17 @@ select * from t1;
 a	b
 0	2
 drop table t1;
+create table t1 (a int, b varchar(10), key b(b(5))) engine=myisam;
+create table t2 (a int, b varchar(10)) engine=myisam;
+insert into t1 values ( 1, 'abcd1e');
+insert into t1 values ( 2, 'abcd2e');
+insert into t2 values ( 1, 'abcd1e');
+insert into t2 values ( 2, 'abcd2e');
+analyze table t1,t2;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+test.t2	analyze	status	OK
+update t1, t2 set t1.a = t2.a where t2.b = t1.b;
+show warnings;
+Level	Code	Message
+drop table t1, t2;
diff --git a/mysql-test/t/update.test b/mysql-test/t/update.test
index 8eb3a924ee3..6a90fb95760 100644
--- a/mysql-test/t/update.test
+++ b/mysql-test/t/update.test
@@ -189,3 +189,15 @@ insert into t1 values (0, '1');
 update t1 set b = b + 1 where a = 0;
 select * from t1;
 drop table t1;
+
+# BUG#9103 "Erroneous data truncation warnings on multi-table updates"
+create table t1 (a int, b varchar(10), key b(b(5))) engine=myisam;
+create table t2 (a int, b varchar(10)) engine=myisam;
+insert into t1 values ( 1, 'abcd1e');
+insert into t1 values ( 2, 'abcd2e');
+insert into t2 values ( 1, 'abcd1e');
+insert into t2 values ( 2, 'abcd2e');
+analyze table t1,t2;
+update t1, t2 set t1.a = t2.a where t2.b = t1.b;
+show warnings;
+drop table t1, t2;
diff --git a/sql/opt_range.cc b/sql/opt_range.cc
index 2ced24f87bb..1cbbaf7c3c4 100644
--- a/sql/opt_range.cc
+++ b/sql/opt_range.cc
@@ -5532,7 +5532,7 @@ QUICK_RANGE_SELECT *get_quick_select_for_ref(THD *thd, TABLE *table,
     goto err;
   }
 
-  if (cp_buffer_from_ref(ref) && thd->is_fatal_error ||
+  if (cp_buffer_from_ref(thd,ref) && thd->is_fatal_error ||
       !(range= new QUICK_RANGE()))
     goto err;                                   // out of memory
 
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index f380876577a..381e94ae53f 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -9583,7 +9583,7 @@ join_read_const(JOIN_TAB *tab)
   if (table->status & STATUS_GARBAGE)		// If first read
   {
     table->status= 0;
-    if (cp_buffer_from_ref(&tab->ref))
+    if (cp_buffer_from_ref(tab->join->thd, &tab->ref))
       error=HA_ERR_KEY_NOT_FOUND;
     else
     {
@@ -9647,7 +9647,7 @@ join_read_always_key(JOIN_TAB *tab)
 
   if (!table->file->inited)
     table->file->ha_index_init(tab->ref.key);
-  if (cp_buffer_from_ref(&tab->ref))
+  if (cp_buffer_from_ref(tab->join->thd, &tab->ref))
     return -1;
   if ((error=table->file->index_read(table->record[0],
 				     tab->ref.key_buff,
@@ -9674,7 +9674,7 @@ join_read_last_key(JOIN_TAB *tab)
 
   if (!table->file->inited)
     table->file->ha_index_init(tab->ref.key);
-  if (cp_buffer_from_ref(&tab->ref))
+  if (cp_buffer_from_ref(tab->join->thd, &tab->ref))
     return -1;
   if ((error=table->file->index_read_last(table->record[0],
 					  tab->ref.key_buff,
@@ -9848,7 +9848,7 @@ join_ft_read_first(JOIN_TAB *tab)
   if (!table->file->inited)
     table->file->ha_index_init(tab->ref.key);
 #if NOT_USED_YET
-  if (cp_buffer_from_ref(&tab->ref))       // as ft-key doesn't use store_key's
+  if (cp_buffer_from_ref(tab->join->thd, &tab->ref)) // as ft-key doesn't use store_key's
     return -1;                             // see also FT_SELECT::init()
 #endif
   table->file->ft_init();
@@ -11609,7 +11609,8 @@ cmp_buffer_with_ref(JOIN_TAB *tab)
   {
     memcpy(tab->ref.key_buff2, tab->ref.key_buff, tab->ref.key_length);
   }
-  if ((tab->ref.key_err=cp_buffer_from_ref(&tab->ref)) || diff)
+  if ((tab->ref.key_err= cp_buffer_from_ref(tab->join->thd, &tab->ref)) || 
+      diff)
     return 1;
   return memcmp(tab->ref.key_buff2, tab->ref.key_buff, tab->ref.key_length)
     != 0;
@@ -11617,11 +11618,17 @@ cmp_buffer_with_ref(JOIN_TAB *tab)
 
 
 bool
-cp_buffer_from_ref(TABLE_REF *ref)
+cp_buffer_from_ref(THD *thd, TABLE_REF *ref)
 {
+  enum enum_check_fields save_count_cuted_fields= thd->count_cuted_fields;
+  thd->count_cuted_fields= CHECK_FIELD_IGNORE;
   for (store_key **copy=ref->key_copy ; *copy ; copy++)
     if ((*copy)->copy())
+    {
+      thd->count_cuted_fields= save_count_cuted_fields;
       return 1;					// Something went wrong
+    }
+  thd->count_cuted_fields= save_count_cuted_fields;
   return 0;
 }
 
diff --git a/sql/sql_select.h b/sql/sql_select.h
index e9397925b6a..c9a9b26d1b4 100644
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@@ -520,7 +520,7 @@ public:
   const char *name() const { return "const"; }
 };
 
-bool cp_buffer_from_ref(TABLE_REF *ref);
+bool cp_buffer_from_ref(THD *thd, TABLE_REF *ref);
 bool error_if_full_join(JOIN *join);
 int report_error(TABLE *table, int error);
 int safe_index_read(JOIN_TAB *tab);