diff --git a/src/filters.cc b/src/filters.cc
index 7b1d95e6..453f95e3 100644
--- a/src/filters.cc
+++ b/src/filters.cc
@@ -40,7 +40,7 @@ void cleanup_whitespaces(Buffer& buffer, Modification& modification)
 
 void expand_tabulations(Buffer& buffer, Modification& modification)
 {
-    const int tabstop = buffer.option_manager()["tabstop"];
+    const int tabstop = buffer.option_manager()["tabstop"].as_int();
     if (modification.type == Modification::Insert and
         modification.content == "\t")
     {
diff --git a/src/highlighters.cc b/src/highlighters.cc
index 45cc95e5..72c633bd 100644
--- a/src/highlighters.cc
+++ b/src/highlighters.cc
@@ -106,7 +106,7 @@ HighlighterAndId colorize_regex_factory(Window& window,
 
 void expand_tabulations(Window& window, DisplayBuffer& display_buffer)
 {
-    const int tabstop = window.option_manager()["tabstop"];
+    const int tabstop = window.option_manager()["tabstop"].as_int();
     for (auto atom_it = display_buffer.begin();
          atom_it != display_buffer.end(); ++atom_it)
     {
diff --git a/src/option_manager.hh b/src/option_manager.hh
index 4309abed..91f35c08 100644
--- a/src/option_manager.hh
+++ b/src/option_manager.hh
@@ -28,8 +28,8 @@ public:
     Option& operator=(int value) { m_value = int_to_str(value); return *this; }
     Option& operator=(const String& value) { m_value = value; return *this; }
 
-    operator int() const { return atoi(m_value.c_str()); }
-    operator String() const { return m_value; }
+    int    as_int()    const  { return atoi(m_value.c_str()); }
+    String as_string() const { return m_value; }
 private:
     String m_value;
 };