diff --git a/src/context.hh b/src/context.hh
index 05acef73..ecca3137 100644
--- a/src/context.hh
+++ b/src/context.hh
@@ -32,7 +32,7 @@ struct Context
             throw runtime_error("no buffer in context");
         return m_editor->buffer();
     }
-    bool has_buffer() const { return m_editor; }
+    bool has_buffer() const { return (bool)m_editor; }
 
     Editor& editor() const
     {
@@ -40,7 +40,7 @@ struct Context
             throw runtime_error("no editor in context");
         return *m_editor.get();
     }
-    bool has_editor() const { return m_editor; }
+    bool has_editor() const { return (bool)m_editor; }
 
     Window& window() const
     {
@@ -48,7 +48,7 @@ struct Context
             throw runtime_error("no window in context");
         return *dynamic_cast<Window*>(m_editor.get());
     }
-    bool has_window() const { return m_editor and dynamic_cast<Window*>(m_editor.get()); }
+    bool has_window() const { return (bool)m_editor and dynamic_cast<Window*>(m_editor.get()); }
 
     Client& client() const
     {
@@ -56,7 +56,7 @@ struct Context
             throw runtime_error("no client in context");
         return *m_client;
     }
-    bool has_client() const { return m_client; }
+    bool has_client() const { return (bool)m_client; }
 
     UserInterface& ui() const
     {
@@ -64,7 +64,7 @@ struct Context
             throw runtime_error("no user interface in context");
         return *m_ui;
     }
-    bool has_ui() const { return m_ui; }
+    bool has_ui() const { return (bool)m_ui; }
 
     void change_editor(Editor& editor)
     {
diff --git a/src/units.hh b/src/units.hh
index b9def254..f5137e99 100644
--- a/src/units.hh
+++ b/src/units.hh
@@ -71,6 +71,7 @@ public:
     { return !m_value; }
 
     explicit constexpr operator ValueType() const { return m_value; }
+    explicit constexpr operator bool() const { return m_value; }
 private:
    ValueType m_value;
 };
diff --git a/src/utils.hh b/src/utils.hh
index 92c09767..73bd6276 100644
--- a/src/utils.hh
+++ b/src/utils.hh
@@ -54,8 +54,6 @@ T* Singleton<T>::ms_instance = nullptr;
 
 // *** safe_ptr: objects that assert nobody references them when they die ***
 
-typedef void* (*unspecified_bool_type)();
-
 template<typename T>
 class safe_ptr
 {
@@ -106,7 +104,7 @@ public:
 
    T* get() const { return m_ptr; }
 
-   operator unspecified_bool_type() const { return (unspecified_bool_type)(m_ptr); }
+   explicit operator bool() const { return m_ptr; }
 
 private:
    T* m_ptr;