diff --git a/Misc/NEWS b/Misc/NEWS
index 4b326ff98e0..06223600ac2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -13,6 +13,8 @@ Core and Builtins
 - Issue #19255: The builtins module is restored to initial value before
   cleaning other modules.  The sys and builtins modules are cleaned last.
 
+- Issue #20588: Make Python-ast.c C89 compliant.
+
 - Issue #20437: Fixed 22 potential bugs when deleting objects references.
 
 - Issue #20500: Displaying an exception at interpreter shutdown no longer
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index 80e432a3e96..d6086e68bf2 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -1203,10 +1203,14 @@ PyObject* PyAST_mod2obj(mod_ty t)
 mod_ty PyAST_obj2mod(PyObject* ast, PyArena* arena, int mode)
 {
     mod_ty res;
-    PyObject *req_type[] = {(PyObject*)Module_type, (PyObject*)Expression_type,
-                            (PyObject*)Interactive_type};
+    PyObject *req_type[3];
     char *req_name[] = {"Module", "Expression", "Interactive"};
     int isinstance;
+
+    req_type[0] = (PyObject*)Module_type;
+    req_type[1] = (PyObject*)Expression_type;
+    req_type[2] = (PyObject*)Interactive_type;
+
     assert(0 <= mode && mode <= 2);
 
     if (!init_types())
diff --git a/Python/Python-ast.c b/Python/Python-ast.c
index e07a93fee8f..44fdafc50ae 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -7023,10 +7023,14 @@ PyObject* PyAST_mod2obj(mod_ty t)
 mod_ty PyAST_obj2mod(PyObject* ast, PyArena* arena, int mode)
 {
     mod_ty res;
-    PyObject *req_type[] = {(PyObject*)Module_type, (PyObject*)Expression_type,
-                            (PyObject*)Interactive_type};
+    PyObject *req_type[3];
     char *req_name[] = {"Module", "Expression", "Interactive"};
     int isinstance;
+
+    req_type[0] = (PyObject*)Module_type;
+    req_type[1] = (PyObject*)Expression_type;
+    req_type[2] = (PyObject*)Interactive_type;
+
     assert(0 <= mode && mode <= 2);
 
     if (!init_types())