diff --git a/mysql-test/r/type_newdecimal.result b/mysql-test/r/type_newdecimal.result
index 901297288af..f3c7e45de39 100644
--- a/mysql-test/r/type_newdecimal.result
+++ b/mysql-test/r/type_newdecimal.result
@@ -1428,6 +1428,19 @@ f1
 20101112000000.000014
 101112.000000
 drop table t1;
+select cast(19999999999999999999 as unsigned);
+cast(19999999999999999999 as unsigned)
+18446744073709551615
+Warnings:
+Error	1292	Truncated incorrect DECIMAL value: ''
+create table t1(a decimal(18));
+insert into t1 values(123456789012345678);
+alter table t1 modify column a decimal(19);
+select * from t1;
+a
+123456789012345678
+drop table t1;
+End of 5.0 tests
 select cast(143.481 as decimal(4,1));
 cast(143.481 as decimal(4,1))
 143.5
@@ -1455,8 +1468,3 @@ Error	1264	Out of range value for column 'cast(-13.4 as decimal(2,1))' at row 1
 select cast(98.6 as decimal(2,0));
 cast(98.6 as decimal(2,0))
 99
-select cast(19999999999999999999 as unsigned);
-cast(19999999999999999999 as unsigned)
-18446744073709551615
-Warnings:
-Error	1292	Truncated incorrect DECIMAL value: ''
diff --git a/mysql-test/t/type_newdecimal.test b/mysql-test/t/type_newdecimal.test
index f16e5dec40c..b8c05d62720 100644
--- a/mysql-test/t/type_newdecimal.test
+++ b/mysql-test/t/type_newdecimal.test
@@ -1126,6 +1126,22 @@ insert into t1 values (CAST('10:11:12' AS time));
 select * from t1;
 drop table t1;
 
+#
+# Bug #8663 (cant use bigint as input to CAST)
+#
+select cast(19999999999999999999 as unsigned);
+
+#
+# Bug #24558: Increasing decimal column length causes data loss
+#
+create table t1(a decimal(18));
+insert into t1 values(123456789012345678);
+alter table t1 modify column a decimal(19);
+select * from t1;
+drop table t1;
+
+--echo End of 5.0 tests
+
 #
 # Bug#16172 DECIMAL data type processed incorrectly
 #
@@ -1136,8 +1152,3 @@ select cast(-3.4 as decimal(2,1));
 select cast(99.6 as decimal(2,0));
 select cast(-13.4 as decimal(2,1));
 select cast(98.6 as decimal(2,0));
-
-# Bug #8663 (cant use bigint as input to CAST)
-#
-select cast(19999999999999999999 as unsigned);
-
diff --git a/sql/field_conv.cc b/sql/field_conv.cc
index 805aba01754..88d36615668 100644
--- a/sql/field_conv.cc
+++ b/sql/field_conv.cc
@@ -336,6 +336,13 @@ static void do_field_real(Copy_field *copy)
 }
 
 
+static void do_field_decimal(Copy_field *copy)
+{
+  my_decimal value;
+  copy->to_field->store_decimal(copy->from_field->val_decimal(&value));
+}
+
+
 /*
   string copy for single byte characters set when to string is shorter than
   from string
@@ -580,6 +587,8 @@ void (*Copy_field::get_copy_func(Field *to,Field *from))(Copy_field*)
     if (to->real_type() == MYSQL_TYPE_BIT ||
         from->real_type() == MYSQL_TYPE_BIT)
       return do_field_int;
+    if (to->result_type() == DECIMAL_RESULT)
+      return do_field_decimal;
     // Check if identical fields
     if (from->result_type() == STRING_RESULT)
     {