diff --git a/kernel/write.c b/kernel/write.c
index 6c77f5f..53ec93b 100644
--- a/kernel/write.c
+++ b/kernel/write.c
@@ -40,6 +40,8 @@ void type_writer(zval *value, zend_long row, zend_long columns, xls_resource_wri
 
             format_set_num_format(value_format, ZSTR_VAL(format));
             WORKSHEET_WRITER_EXCEPTION(worksheet_write_number(res->worksheet, lxw_row, lxw_col, (double)zval_get_long(value), value_format));
+
+            free(value_format);
             return;
         }
 
@@ -55,6 +57,8 @@ void type_writer(zval *value, zend_long row, zend_long columns, xls_resource_wri
             format_set_num_format(value_format, ZSTR_VAL(format));
 
             WORKSHEET_WRITER_EXCEPTION(worksheet_write_number(res->worksheet, lxw_row, lxw_col, (double)zval_get_long(value), value_format));
+
+            free(value_format);
             return;
         }
 
@@ -67,6 +71,7 @@ void type_writer(zval *value, zend_long row, zend_long columns, xls_resource_wri
             format_set_num_format(value_format, ZSTR_VAL(format));
 
             WORKSHEET_WRITER_EXCEPTION(worksheet_write_number(res->worksheet, lxw_row, lxw_col, zval_get_double(value), value_format));
+            free(value_format);
             return;
         }
 
@@ -82,6 +87,7 @@ void type_writer(zval *value, zend_long row, zend_long columns, xls_resource_wri
             format_set_num_format(value_format, ZSTR_VAL(format));
 
             WORKSHEET_WRITER_EXCEPTION(worksheet_write_number(res->worksheet, lxw_row, lxw_col, zval_get_double(value), value_format));
+            free(value_format);
             return;
         }
 
@@ -263,6 +269,8 @@ void datetime_writer(lxw_datetime *datetime, zend_long row, zend_long columns, z
 
     format_set_num_format(value_format, ZSTR_VAL(format));
     worksheet_write_datetime(res->worksheet, (lxw_row_t)row, (lxw_col_t)columns, datetime, value_format);
+
+    free(value_format);
 }
 
 /*