diff --git a/dbms/src/Functions/FunctionsConversion.h b/dbms/src/Functions/FunctionsConversion.h
index a83ae586d80..b0fcc0103d6 100644
--- a/dbms/src/Functions/FunctionsConversion.h
+++ b/dbms/src/Functions/FunctionsConversion.h
@@ -1632,6 +1632,7 @@ private:
         using ToDataType = DataTypeDecimal<FieldType>;
 
         TypeIndex type_index = from_type->getTypeId();
+        UInt32 precision = to_type->getPrecision();
         UInt32 scale = to_type->getScale();
 
         WhichDataType which(type_index);
@@ -1645,9 +1646,9 @@ private:
             throw Exception{"Conversion from " + from_type->getName() + " to " + to_type->getName() + " is not supported",
                 ErrorCodes::CANNOT_CONVERT_TYPE};
 
-        return [type_index, scale] (Block & block, const ColumnNumbers & arguments, const size_t result, size_t input_rows_count)
+        return [type_index, precision, scale] (Block & block, const ColumnNumbers & arguments, const size_t result, size_t input_rows_count)
         {
-            callOnIndexAndDataType<ToDataType>(type_index, [&](const auto & types) -> bool
+            auto res = callOnIndexAndDataType<ToDataType>(type_index, [&](const auto & types) -> bool
             {
                 using Types = std::decay_t<decltype(types)>;
                 using LeftDataType = typename Types::LeftType;
@@ -1656,6 +1657,14 @@ private:
                 ConvertImpl<LeftDataType, RightDataType, NameCast>::execute(block, arguments, result, input_rows_count, scale);
                 return true;
             });
+
+            /// Additionally check if callOnIndexAndDataType wasn't called at all.
+            if (!res)
+            {
+                auto to = DataTypeDecimal<FieldType>(precision, scale);
+                throw Exception{"Conversion from " + std::string(getTypeName(type_index)) + " to " + to.getName() +
+                                " is not supported", ErrorCodes::CANNOT_CONVERT_TYPE};
+            }
         };
     }
 
@@ -2022,6 +2031,11 @@ private:
 
                 const auto & tmp_res = tmp_block.getByPosition(tmp_res_index);
 
+                /// May happen in fuzzy tests. For debug purpose.
+                if (!tmp_res.column)
+                    throw Exception("Couldn't convert " + block.getByPosition(arguments[0]).type->getName() + " to "
+                                    + nested_type->getName() + " in " + " prepareRemoveNullable wrapper.", ErrorCodes::LOGICAL_ERROR);
+
                 res.column = wrapInNullable(tmp_res.column, Block({block.getByPosition(arguments[0]), tmp_res}), {0}, 1, input_rows_count);
             };
         }