diff --git a/infra/sandboxes/supervisor/src/computer-spec.test.ts b/infra/sandboxes/supervisor/src/computer-spec.test.ts
index 7a0f125..8b59175 100644
--- a/infra/sandboxes/supervisor/src/computer-spec.test.ts
+++ b/infra/sandboxes/supervisor/src/computer-spec.test.ts
@@ -669,6 +669,17 @@ describe("computer resource limits", () => {
     expect(HostConfig.PidsLimit).toBe(2048);
   });
 
+  it("falls back to the defaults when a limit is set but blank", () => {
+    // .env.example ships these keys with no value, which loads as "" rather than undefined.
+    for (const value of ["", "  "]) {
+      for (const k of KEYS) process.env[k] = value;
+      const { HostConfig } = containerCreateOptions(createInput);
+      expect(HostConfig.Memory).toBe(2 * 1024 ** 3);
+      expect(HostConfig.NanoCpus).toBe(2 * 1e9);
+      expect(HostConfig.PidsLimit).toBe(2048);
+    }
+  });
+
   it("pins MemorySwap to Memory so the ceiling cannot be swapped past", () => {
     process.env.RAKAZO_COMPUTER_MEMORY = "1536m";
     const { HostConfig } = containerCreateOptions(createInput);
diff --git a/infra/sandboxes/supervisor/src/computer-spec.ts b/infra/sandboxes/supervisor/src/computer-spec.ts
index 66c8f11..8e70f9b 100644
--- a/infra/sandboxes/supervisor/src/computer-spec.ts
+++ b/infra/sandboxes/supervisor/src/computer-spec.ts
@@ -113,19 +113,25 @@ function parsePidsLimit(name: string, raw: string): number {
   return value;
 }
 
+/** An unset or blank variable (as .env.example ships these) means the default. */
+function limitSetting(name: string, fallback: string): string {
+  const value = process.env[name];
+  return value?.trim() ? value : fallback;
+}
+
 /** The host resource ceilings applied to every bot computer. */
 export function computerResourceLimits() {
   const memoryBytes = parseMemoryBytes(
     "RAKAZO_COMPUTER_MEMORY",
-    process.env.RAKAZO_COMPUTER_MEMORY ?? DEFAULT_COMPUTER_MEMORY,
+    limitSetting("RAKAZO_COMPUTER_MEMORY", DEFAULT_COMPUTER_MEMORY),
   );
   const nanoCpus = parseNanoCpus(
     "RAKAZO_COMPUTER_CPUS",
-    process.env.RAKAZO_COMPUTER_CPUS ?? DEFAULT_COMPUTER_CPUS,
+    limitSetting("RAKAZO_COMPUTER_CPUS", DEFAULT_COMPUTER_CPUS),
   );
   const pidsLimit = parsePidsLimit(
     "RAKAZO_COMPUTER_PIDS_LIMIT",
-    process.env.RAKAZO_COMPUTER_PIDS_LIMIT ?? DEFAULT_COMPUTER_PIDS_LIMIT,
+    limitSetting("RAKAZO_COMPUTER_PIDS_LIMIT", DEFAULT_COMPUTER_PIDS_LIMIT),
   );
   return {
     // Memory and MemorySwap are set together: leaving MemorySwap unset lets the