diff --git a/mysql-test/r/sp.result b/mysql-test/r/sp.result
index 0751363a6ea..746cd8f00d4 100644
--- a/mysql-test/r/sp.result
+++ b/mysql-test/r/sp.result
@@ -4929,4 +4929,35 @@ j
 drop table t3|
 drop view v1|
 drop function bug12472|
+DROP FUNCTION IF EXISTS bug18589_f1|
+DROP PROCEDURE IF EXISTS bug18589_p1|
+DROP PROCEDURE IF EXISTS bug18589_p2|
+CREATE FUNCTION bug18589_f1(arg TEXT) RETURNS TEXT
+BEGIN
+RETURN CONCAT(arg, "");
+END|
+CREATE PROCEDURE bug18589_p1(arg TEXT, OUT ret TEXT)
+BEGIN
+SET ret = CONCAT(arg, "");
+END|
+CREATE PROCEDURE bug18589_p2(arg TEXT)
+BEGIN
+DECLARE v TEXT;
+CALL bug18589_p1(arg, v);
+SELECT v;
+END|
+SELECT bug18589_f1(REPEAT("a", 767))|
+bug18589_f1(REPEAT("a", 767))
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+SET @bug18589_v1 = ""|
+CALL bug18589_p1(REPEAT("a", 767), @bug18589_v1)|
+SELECT @bug18589_v1|
+@bug18589_v1
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+CALL bug18589_p2(REPEAT("a", 767))|
+v
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+DROP FUNCTION bug18589_f1|
+DROP PROCEDURE bug18589_p1|
+DROP PROCEDURE bug18589_p2|
 drop table t1,t2;
diff --git a/mysql-test/t/sp.test b/mysql-test/t/sp.test
index a5c3e60b9ca..9995ff5a9ad 100644
--- a/mysql-test/t/sp.test
+++ b/mysql-test/t/sp.test
@@ -5796,6 +5796,53 @@ drop view v1|
 drop function bug12472|
 
 
+#
+# BUG#18587: Function that accepts and returns TEXT garbles data if longer than
+# 766 chars
+#
+
+# Prepare.
+
+--disable_warnings
+DROP FUNCTION IF EXISTS bug18589_f1|
+DROP PROCEDURE IF EXISTS bug18589_p1|
+DROP PROCEDURE IF EXISTS bug18589_p2|
+--enable_warnings
+
+CREATE FUNCTION bug18589_f1(arg TEXT) RETURNS TEXT
+BEGIN
+  RETURN CONCAT(arg, "");
+END|
+
+CREATE PROCEDURE bug18589_p1(arg TEXT, OUT ret TEXT)
+BEGIN
+  SET ret = CONCAT(arg, "");
+END|
+
+CREATE PROCEDURE bug18589_p2(arg TEXT)
+BEGIN
+  DECLARE v TEXT;
+  CALL bug18589_p1(arg, v);
+  SELECT v;
+END|
+
+# Test case.
+
+SELECT bug18589_f1(REPEAT("a", 767))|
+
+SET @bug18589_v1 = ""|
+CALL bug18589_p1(REPEAT("a", 767), @bug18589_v1)|
+SELECT @bug18589_v1|
+
+CALL bug18589_p2(REPEAT("a", 767))|
+
+# Cleanup.
+
+DROP FUNCTION bug18589_f1|
+DROP PROCEDURE bug18589_p1|
+DROP PROCEDURE bug18589_p2|
+
+
 #
 # BUG#NNNN: New bug synopsis
 #
diff --git a/sql/field_conv.cc b/sql/field_conv.cc
index 895f022624c..4e977c06180 100644
--- a/sql/field_conv.cc
+++ b/sql/field_conv.cc
@@ -642,7 +642,8 @@ void (*Copy_field::get_copy_func(Field *to,Field *from))(Copy_field*)
 
 void field_conv(Field *to,Field *from)
 {
-  if (to->real_type() == from->real_type())
+  if (to->real_type() == from->real_type() &&
+      !(to->type() == FIELD_TYPE_BLOB && to->table->copy_blobs))
   {
     if (to->pack_length() == from->pack_length() &&
         !(to->flags & UNSIGNED_FLAG && !(from->flags & UNSIGNED_FLAG)) &&
diff --git a/sql/item_func.cc b/sql/item_func.cc
index 0447ab115ec..603a00947dd 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -4735,6 +4735,7 @@ Item_func_sp::sp_result_field(void) const
     dummy_table->alias = empty_name;
     dummy_table->maybe_null = maybe_null;
     dummy_table->in_use= current_thd;
+    dummy_table->copy_blobs= TRUE;
     share->table_cache_key = empty_name;
     share->table_name = empty_name;
   }