--- a/python/mozbuild/mozbuild/frontend/reader.py
+++ b/python/mozbuild/mozbuild/frontend/reader.py
@@ -465,17 +465,17 @@ class TemplateFunction:
                 return node
 
             def c(new_node):
                 return ast.copy_location(new_node, node)
 
             return c(
                 ast.Subscript(
                     value=c(ast.Name(id=self._global_name, ctx=ast.Load())),
-                    slice=c(ast.Index(value=c(ast.Str(s=node.id)))),
+                    slice=c(ast.Index(value=c(ast.Constant(value=node.id)))),
                     ctx=node.ctx,
                 )
             )
 
 
 class SandboxValidationError(Exception):
     """Represents an error encountered when validating sandbox results."""
 
@@ -1034,33 +1034,33 @@ class BuildReader:
                 # We need to branch to deal with python version differences.
                 if isinstance(target.slice, ast.Constant):
                     # Python >= 3.9
                     assert isinstance(target.slice.value, str)
                     key = target.slice.value
                 else:
                     # Others
                     assert isinstance(target.slice, ast.Index)
-                    assert isinstance(target.slice.value, ast.Str)
-                    key = target.slice.value.s
+                    assert isinstance(target.slice.value, ast.Constant)
+                    key = target.slice.value.value
             elif isinstance(target, ast.Attribute):
                 assert isinstance(target.attr, str)
                 key = target.attr
 
             return name, key
 
         def assigned_values(node):
             value = node.value
             if isinstance(value, ast.List):
                 for v in value.elts:
-                    assert isinstance(v, ast.Str)
-                    yield v.s
+                    assert isinstance(v, ast.Constant)
+                    yield v.value
             else:
-                assert isinstance(value, ast.Str)
-                yield value.s
+                assert isinstance(value, ast.Constant)
+                yield value.value
 
         assignments = []
 
         class Visitor(ast.NodeVisitor):
             def helper(self, node):
                 name, key = assigned_variable(node)
                 if not name:
                     return

--- a/python/mozbuild/mozbuild/vendor/rewrite_mozbuild.py
+++ b/python/mozbuild/mozbuild/vendor/rewrite_mozbuild.py
@@ -322,25 +322,23 @@ def assignment_node_to_source_filename_l
     If this happens, we'll return an empty list. The consequence of this is that we
     won't be able to match a file against this list, so we may not be able to add it.
 
     (But if the file matches a generated list, perhaps it will be included in the
     Sources list automatically?)
     """
     if isinstance(node.value, ast.List) and "elts" in node.value._fields:
         for f in node.value.elts:
-            if not isinstance(f, ast.Constant) and not isinstance(f, ast.Str):
+            if not isinstance(f, ast.Constant):
                 log(
                     "Found non-constant source file name in list: ",
                     ast_get_source_segment(code, f),
                 )
                 return []
-        return [
-            f.value if isinstance(f, ast.Constant) else f.s for f in node.value.elts
-        ]
+        return [f.value for f in node.value.elts]
     elif isinstance(node.value, ast.ListComp):
         # SOURCES += [f for f in foo if blah]
         log("Could not find the files for " + ast_get_source_segment(code, node.value))
     elif isinstance(node.value, ast.Name) or isinstance(node.value, ast.Subscript):
         # SOURCES += other_var
         # SOURCES += files['X64_SOURCES']
         log("Could not find the files for " + ast_get_source_segment(code, node))
     elif isinstance(node.value, ast.Call):