diff --git a/codegen/valaccodemethodmodule.vala b/codegen/valaccodemethodmodule.vala
index d147eb1..1347a26 100644
--- a/codegen/valaccodemethodmodule.vala
+++ b/codegen/valaccodemethodmodule.vala
@@ -476,6 +476,7 @@ public abstract class Vala.CCodeMethodModule : CCodeStructModule {
 
 					// coroutine body
 					ccode.add_label ("_state_0");
+					ccode.add_assignment (new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_in_progress_"), new CCodeConstant ("0"));
 				}
 
 				if (m.closure) {
diff --git a/codegen/valagasyncmodule.vala b/codegen/valagasyncmodule.vala
index 928e67b..d0c8001 100644
--- a/codegen/valagasyncmodule.vala
+++ b/codegen/valagasyncmodule.vala
@@ -28,6 +28,7 @@ public class Vala.GAsyncModule : GtkModule {
 		var data = new CCodeStruct ("_" + dataname);
 
 		data.add_field ("int", "_state_");
+		data.add_field ("int", "_state_in_progress_");
 		data.add_field ("GObject*", "_source_object_");
 		data.add_field ("GAsyncResult*", "_res_");
 		data.add_field ("GSimpleAsyncResult*", "_async_result");
@@ -663,10 +664,25 @@ public class Vala.GAsyncModule : GtkModule {
 
 		if (stmt.yield_expression == null) {
 			int state = next_coroutine_state++;
-
+			ccode.open_if(
+				new CCodeBinaryExpression(CCodeBinaryOperator.INEQUALITY, 
+					new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_"), 
+					new CCodeConstant (state.to_string ()) ) );
 			ccode.add_assignment (new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_"), new CCodeConstant (state.to_string ()));
 			ccode.add_return (new CCodeConstant ("FALSE"));
+			ccode.add_else();
+			ccode.add_statement (new CCodeComment ("callback to wakeup yield is already called, so no wait"));
+			ccode.close();
+			
 			ccode.add_label ("_state_%d".printf (state));
+			ccode.open_if(
+				new CCodeBinaryExpression(CCodeBinaryOperator.EQUALITY, 
+					new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_in_progress_"), 
+					new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_") ) );
+			ccode.add_statement (new CCodeComment ("callback is called too early before that yield stantment is really reached"));
+			ccode.add_return (new CCodeConstant ("FALSE"));
+			ccode.close();
+			ccode.add_assignment (new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_in_progress_"), new CCodeConstant (state.to_string ()));
 			ccode.add_statement (new CCodeEmptyStatement ());
 
 			return;