diff --git a/mysql-test/r/type_newdecimal.result b/mysql-test/r/type_newdecimal.result
index e5fbf158a8b..819e41f41c5 100644
--- a/mysql-test/r/type_newdecimal.result
+++ b/mysql-test/r/type_newdecimal.result
@@ -1908,4 +1908,16 @@ group by PAY.id + 1;
 mult	v_net_with_discount	v_total
 1.0000	27.18	27.180000
 DROP TABLE currencies, payments, sub_tasks;
+#
+# BUG#52171: distinct aggregates on unsigned decimal fields trigger assertions
+#
+CREATE TABLE t1 (a DECIMAL(4,4) UNSIGNED);
+INSERT INTO t1 VALUES (0);
+SELECT AVG(DISTINCT a) FROM t1;
+AVG(DISTINCT a)
+0.00000000
+SELECT SUM(DISTINCT a) FROM t1;
+SUM(DISTINCT a)
+0.0000
+DROP TABLE t1;
 End of 5.1 tests
diff --git a/mysql-test/t/type_newdecimal.test b/mysql-test/t/type_newdecimal.test
index 3f418a339cc..bd70e64b1ad 100644
--- a/mysql-test/t/type_newdecimal.test
+++ b/mysql-test/t/type_newdecimal.test
@@ -1509,5 +1509,14 @@ group by PAY.id + 1;
 
 DROP TABLE currencies, payments, sub_tasks;
 
+--echo #
+--echo # BUG#52171: distinct aggregates on unsigned decimal fields trigger assertions
+--echo #
+
+CREATE TABLE t1 (a DECIMAL(4,4) UNSIGNED);
+INSERT INTO t1 VALUES (0);
+SELECT AVG(DISTINCT a) FROM t1;
+SELECT SUM(DISTINCT a) FROM t1;
+DROP TABLE t1;
 
 --echo End of 5.1 tests
diff --git a/sql/field.cc b/sql/field.cc
index fc55426b177..113b4752648 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -9104,7 +9104,7 @@ void Create_field::init_for_tmp_table(enum_field_types sql_type_arg,
   case MYSQL_TYPE_NEWDECIMAL:
   case MYSQL_TYPE_FLOAT:
   case MYSQL_TYPE_DOUBLE:
-    pack_flag= FIELDFLAG_DECIMAL | FIELDFLAG_NUMBER |
+    pack_flag= FIELDFLAG_NUMBER |
       (decimals_arg & FIELDFLAG_MAX_DEC) << FIELDFLAG_DEC_SHIFT;
     break;
 
@@ -9153,12 +9153,13 @@ void Create_field::init_for_tmp_table(enum_field_types sql_type_arg,
     (maybe_null ? FIELDFLAG_MAYBE_NULL : 0) |
     (is_unsigned ? 0 : FIELDFLAG_DECIMAL);
 
-  DBUG_PRINT("debug", ("pack_flag: %s%s%s%s%s, pack_type: %d",
+  DBUG_PRINT("debug", ("pack_flag: %s%s%s%s%s%s, pack_type: %d",
                        FLAGSTR(pack_flag, FIELDFLAG_BINARY),
                        FLAGSTR(pack_flag, FIELDFLAG_NUMBER),
                        FLAGSTR(pack_flag, FIELDFLAG_INTERVAL),
                        FLAGSTR(pack_flag, FIELDFLAG_GEOM),
                        FLAGSTR(pack_flag, FIELDFLAG_BLOB),
+                       FLAGSTR(pack_flag, FIELDFLAG_DECIMAL),
                        f_packtype(pack_flag)));
   DBUG_VOID_RETURN;
 }