diff --git a/ast27/Include/asdl.h b/ast27/Include/asdl.h
index 2e5045b4..b8a5d2f2 100644
--- a/ast27/Include/asdl.h
+++ b/ast27/Include/asdl.h
@@ -8,8 +8,10 @@ typedef PyObject * string;
 typedef PyObject * object;
 
 #ifndef __cplusplus
+#ifndef __bool_true_false_are_defined
 typedef enum {false, true} bool;
 #endif
+#endif
 
 /* It would be nice if the code generated by asdl_c.py was completely
    independent of Python, but it is a goal the requires too much work
diff --git a/ast3/Python/ast.c b/ast3/Python/ast.c
index 60b8fdd4..b87a8604 100644
--- a/ast3/Python/ast.c
+++ b/ast3/Python/ast.c
@@ -13,9 +13,12 @@
 #include <assert.h>
 
 // VS 2010 doesn't have <stdbool.h>...
+#ifndef __bool_true_false_are_defined
 typedef int bool;
 #define false 0
 #define true 1
+#endif
+
 
 #if PY_MINOR_VERSION < 6
 static PyObject *