diff --git a/test/packaging/lint-once.test.ts b/test/packaging/lint-once.test.ts
index 9694a61..8137ccc 100644
--- a/test/packaging/lint-once.test.ts
+++ b/test/packaging/lint-once.test.ts
@@ -159,7 +159,7 @@ const MAKE_CONDITIONAL = /^\s*(?:ifeq|ifneq|ifdef|ifndef|else|endif)\b/;
 // not happen. An unresolved reference is left standing verbatim instead, which
 // is the same dead end as any other unfollowed edge rather than a wrong answer.
 const MAKE_ASSIGNMENT = new RegExp(
-    `^([A-Za-z_][A-Za-z0-9_]*)\\s*(?::=|\\?=|=)\\s*(.*)$`,
+    `^(?:(?:export|override)\\s+)*([A-Za-z_][A-Za-z0-9_]*)\\s*(:=|\\?=|=)\\s*(.*)$`,
 );
 const MAKE_VARIABLE_REFERENCE = /\$[({]([A-Za-z_][A-Za-z0-9_]*)[)}]/g;
 
@@ -181,8 +181,13 @@ const makeVariables = (text: string): Map<string, string> => {
         if (inDefine || raw.startsWith("\t")) continue;
         const assignment = MAKE_ASSIGNMENT.exec(raw.replace(/#.*$/, "").trim());
         if (assignment === null) continue;
-        const [, name, value] = assignment;
-        if (name === undefined || value === undefined) continue;
+        const [, name, operator, value] = assignment;
+        if (name === undefined || operator === undefined) continue;
+        if (value === undefined) continue;
+        // `?=` assigns only when the name has no value yet, so the first one
+        // wins where `:=` and `=` let the last one win. Overwriting here would
+        // resolve the reference to a string make never uses.
+        if (operator === "?=" && variables.has(name)) continue;
         // A value that is itself a reference is the recursive case, and is not
         // resolved. Recording it would hand the substitution below a string it
         // cannot finish expanding.