diff --git a/packages/process-utils/src/index.ts b/packages/process-utils/src/index.ts
index 8b8568b47..ce07ccaf0 100644
--- a/packages/process-utils/src/index.ts
+++ b/packages/process-utils/src/index.ts
@@ -177,6 +177,8 @@ export function resolveContainedPath(
   return resolvedCandidatePath;
 }
 
+const VOLTA_RECURSION_GUARD_ENV = "_VOLTA_TOOL_RECURSION";
+
 /**
  * The one answer to "what does a bb-spawned child process inherit": the
  * parent's env minus bb runtime-owned variables (`BB_*`) and `NODE_ENV`,
@@ -194,6 +196,14 @@ export function sanitizeInheritedChildProcessEnv(
     if (key === "NODE_ENV" || key.startsWith("BB_")) {
       continue;
     }
+    // Volta's re-entrancy guard. A Volta package shim sets it on the process
+    // it launches (bb-app), and Volta's own `node`/`npm`/`npx` shims treat its
+    // presence as "do not re-evaluate the platform" and pass through to a
+    // system Node instead. bb children are new contexts, exactly like
+    // `volta run`, which removes the same variable before spawning.
+    if (key === VOLTA_RECURSION_GUARD_ENV) {
+      continue;
+    }
     sanitizedEnv[key] = value;
   }
   if (args.shellPath !== undefined) {