diff --git a/src/Makefile b/src/Makefile
index f927d9e3..f0ac8aa3 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -5,6 +5,17 @@ deps := $(addprefix ., $(sources:.cc=.d))
 CXXFLAGS += -std=c++0x -g -Wall -Wno-reorder -Wno-sign-compare
 LDFLAGS += -lmenu -lncursesw -lboost_regex
 
+debug ?= yes
+ifeq ($(debug),yes)
+    CXXFLAGS += -DKAK_DEBUG
+else
+    ifeq ($(debug),no)
+        CXXFLAGS += -O3
+    else
+        $(error debug should be either yes or no)
+    endif
+endif
+
 kak : $(objects)
 	$(CXX) $(LDFLAGS) $(CXXFLAGS) $(objects) -o $@
 
diff --git a/src/assert.hh b/src/assert.hh
index 182b58a4..52bdcf48 100644
--- a/src/assert.hh
+++ b/src/assert.hh
@@ -16,8 +16,14 @@ void on_assert_failed(const char* message);
 #undef assert
 #endif
 
-#define assert(condition) \
-    if (not (condition)) \
-        on_assert_failed("assert failed \"" #condition "\" at " __FILE__ ":" TOSTRING(__LINE__))
+#ifdef KAK_DEBUG
+    #define assert(condition) \
+        if (not (condition)) \
+            on_assert_failed("assert failed \"" #condition \
+                             "\" at " __FILE__ ":" TOSTRING(__LINE__))
+#else
+    #define assert(condition)
+#endif
+
 
 #endif // assert_hh_INCLUDED
diff --git a/src/buffer.cc b/src/buffer.cc
index 3c919c19..a73f8fd3 100644
--- a/src/buffer.cc
+++ b/src/buffer.cc
@@ -225,6 +225,7 @@ bool Buffer::redo()
 
 void Buffer::check_invariant() const
 {
+#ifdef KAK_DEBUG
     ByteCount start = 0;
     assert(not m_lines.empty());
     for (auto& line : m_lines)
@@ -234,6 +235,7 @@ void Buffer::check_invariant() const
         assert(line.content.back() == '\n');
         start += line.length();
     }
+#endif
 }
 
 void Buffer::do_insert(const BufferIterator& pos, const String& content)
diff --git a/src/commands.cc b/src/commands.cc
index 88271505..c7247016 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -27,11 +27,6 @@
 namespace Kakoune
 {
 
-using namespace std::placeholders;
-
-// berk
-extern bool    quit_requested;
-
 namespace
 {
 
diff --git a/src/editor.cc b/src/editor.cc
index 1567608e..77080312 100644
--- a/src/editor.cc
+++ b/src/editor.cc
@@ -376,6 +376,7 @@ bool Editor::redo()
 
 void Editor::check_invariant() const
 {
+#ifdef KAK_DEBUG
     assert(not m_selections.empty());
     m_selections.check_invariant();
 
@@ -383,6 +384,7 @@ void Editor::check_invariant() const
                                  compare_selections);
     assert(std::is_sorted(m_selections.begin(), it, compare_selections));
     assert(std::is_sorted(it, m_selections.end(), compare_selections));
+#endif
 }
 
 void Editor::begin_edition()
diff --git a/src/parameters_parser.cc b/src/parameters_parser.cc
index cdcfb0c1..1bf1e4d2 100644
--- a/src/parameters_parser.cc
+++ b/src/parameters_parser.cc
@@ -48,9 +48,11 @@ bool ParametersParser::has_option(const String& name) const
 
 const String& ParametersParser::option_value(const String& name) const
 {
+#ifdef KAK_DEBUG
     auto it = m_options.find(name);
     assert(it != m_options.end());
     assert(it->second == true);
+#endif
 
     for (size_t i = 0; i < m_params.size(); ++i)
     {
diff --git a/src/selection.cc b/src/selection.cc
index 77511c00..04ebae81 100644
--- a/src/selection.cc
+++ b/src/selection.cc
@@ -26,10 +26,12 @@ BufferIterator Range::end() const
 
 void Range::check_invariant() const
 {
+#ifdef KAK_DEBUG
     assert(m_first.is_valid());
     assert(m_last.is_valid());
     assert(utf8::is_character_start(m_first));
     assert(utf8::is_character_start(m_last));
+#endif
 }
 
 static void avoid_eol(BufferIterator& it)