diff --git a/mysql-test/r/func_str.result b/mysql-test/r/func_str.result
index 6f8269bdcbd..a17661d26d0 100644
--- a/mysql-test/r/func_str.result
+++ b/mysql-test/r/func_str.result
@@ -1046,4 +1046,10 @@ cast(ltrim('  20.06 ') as decimal(19,2))
 select cast(rtrim(ltrim('  20.06 ')) as decimal(19,2));
 cast(rtrim(ltrim('  20.06 ')) as decimal(19,2))
 20.06
+select conv("18383815659218730760",10,10) + 0;
+conv("18383815659218730760",10,10) + 0
+1.8383815659219e+19
+select "18383815659218730760" + 0;
+"18383815659218730760" + 0
+1.8383815659219e+19
 End of 5.0 tests
diff --git a/mysql-test/t/func_str.test b/mysql-test/t/func_str.test
index dee06231deb..7f809dbc4a1 100644
--- a/mysql-test/t/func_str.test
+++ b/mysql-test/t/func_str.test
@@ -698,4 +698,10 @@ select cast(rtrim('  20.06 ') as decimal(19,2));
 select cast(ltrim('  20.06 ') as decimal(19,2));
 select cast(rtrim(ltrim('  20.06 ')) as decimal(19,2));
 
+#
+# Bug #13975: "same string" + 0 has 2 different results
+#
+select conv("18383815659218730760",10,10) + 0;
+select "18383815659218730760" + 0;
+
 --echo End of 5.0 tests
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index 7d7b62df0dc..90d421a2c68 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -542,7 +542,7 @@ public:
   void fix_length_and_dec()
   {
     collation.set(default_charset());
-    decimals=0; max_length=64;
+    max_length= 64;
   }
 };