diff --git a/src/Columns/ColumnString.cpp b/src/Columns/ColumnString.cpp
index c99de961e74..a250f9f89ad 100644
--- a/src/Columns/ColumnString.cpp
+++ b/src/Columns/ColumnString.cpp
@@ -183,10 +183,12 @@ void ColumnString::expand(const IColumn::Filter & mask, bool inverted)
             if (from < 0)
                 throw Exception("Too many bytes in mask", ErrorCodes::LOGICAL_ERROR);
 
-            int len = offsets_data[from] - offsets_data[from - 1];
-            /// Copy only if it makes sense.
+            size_t len = offsets_data[from] - offsets_data[from - 1];
+
+            /// Copy only if it makes sense. It's important to copy backward, because
+            /// ranges can overlap, but destination is always is more to the right then source
             if (last_offset - len != offsets_data[from - 1])
-                memcpy(&chars_data[last_offset - len], &chars_data[offsets_data[from - 1]], len);
+                std::copy_backward(&chars_data[offsets_data[from - 1]], &chars_data[offsets_data[from]], &chars_data[last_offset]);
             last_offset -= len;
             --from;
         }
diff --git a/src/Columns/MaskOperations.cpp b/src/Columns/MaskOperations.cpp
index 8841564c89e..5433983363b 100644
--- a/src/Columns/MaskOperations.cpp
+++ b/src/Columns/MaskOperations.cpp
@@ -206,7 +206,7 @@ int checkShirtCircuitArguments(const ColumnsWithTypeAndName & arguments)
     int last_short_circuit_argument_index = -1;
     for (size_t i = 0; i != arguments.size(); ++i)
     {
-        if (const auto * column_function = checkAndGetShortCircuitArgument(arguments[i].column))
+        if (checkAndGetShortCircuitArgument(arguments[i].column))
             last_short_circuit_argument_index = i;
     }