diff --git a/codegen/valaccodemethodmodule.vala b/codegen/valaccodemethodmodule.vala
index d147eb1..cbd6e1a 100644
--- a/codegen/valaccodemethodmodule.vala
+++ b/codegen/valaccodemethodmodule.vala
@@ -456,6 +456,14 @@ public abstract class Vala.CCodeMethodModule : CCodeStructModule {
 		if (!m.is_abstract || (m.is_abstract && current_type_symbol is Class)) {
 			if (m.body != null) {
 				if (m.coroutine) {
+					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.open_switch (new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_"));
 
 					// initial coroutine state
@@ -475,7 +483,8 @@ public abstract class Vala.CCodeMethodModule : CCodeStructModule {
 					ccode.close ();
 
 					// coroutine body
-					ccode.add_label ("_state_0");
+					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..6a24300 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");
@@ -200,6 +201,7 @@ public class Vala.GAsyncModule : GtkModule {
 
 		ccode.add_declaration (dataname + "*", new CCodeVariableDeclarator ("_data_"));
 		ccode.add_assignment (data_var, dataalloc);
+		ccode.add_assignment (new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_in_progress_"), new CCodeConstant ("-1"));
 
 		var create_result = new CCodeFunctionCall (new CCodeIdentifier ("g_simple_async_result_new"));
 
@@ -663,10 +665,18 @@ 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.add_assignment (new CCodeMemberAccess.pointer (new CCodeIdentifier ("_data_"), "_state_in_progress_"), new CCodeConstant (state.to_string ()));
 			ccode.add_statement (new CCodeEmptyStatement ());
 
 			return;