diff --git a/.gitignore b/.gitignore
index 7ae1a83..8921232 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 *.ali
 *.o
 build
+obj
 testrunner
 xmlrunner
diff --git a/Makefile b/Makefile
index 6b16642..c01cdca 100644
--- a/Makefile
+++ b/Makefile
@@ -4,19 +4,22 @@ TESTRUNNER=testrunner
 
 PROJECTGPR=async.gpr
 
+release: pre syntax
+	$(GPRBUILD) -p $(PROJECTGPR) -Xmode=release
+
 lib: pre
 	$(GPRBUILD) -p $(PROJECTGPR)
 
-syntax: pre
+syntax: pre lib
 	gnatmake -gnatc -gnat05 -P $(PROJECTGPR)
 
 clean: pre
 	for d in tests/*; do echo "> $$d"; (cd $$d && make clean); done
 	$(GPRCLEAN) $(PROJECTGPR)
-	rm -rf build
+	rm -rf obj
 
 pre:
-	mkdir -p build
+	mkdir -p obj/debug obj/release
 
 test: pre lib
 	for d in tests/*; do echo "> $$d"; (cd $$d && make run); done
diff --git a/async.gpr b/async.gpr
index 72682ac..1d17ff8 100644
--- a/async.gpr
+++ b/async.gpr
@@ -1,12 +1,22 @@
 
 project Async is
+    for Languages use ("Ada");
     for Source_Dirs use ("src");
-    for Object_Dir use "build";
+    for Object_Dir use "obj/" & external ("mode", "debug");
     for Exec_Dir use ".";
 
+    type Mode_Type is ("debug", "release");
+    Mode : Mode_Type := external ("mode", "debug");
+
     package Compiler is
-    for Default_Switches("ada") use
-            ("-O2", "-gnat05");
+        case Mode is
+            when "debug" =>
+                for Default_Switches ("Ada") use
+                        ("-g", "-gnat05");
+            when "release" =>
+                for Default_Switches ("Ada") use
+                        ("-O2", "-gnat05");
+        end case;
     end Compiler;
 end Async;