diff --git a/.changeset/guard-process-group-pgids.md b/.changeset/guard-process-group-pgids.md
new file mode 100644
index 0000000..ead557c
--- /dev/null
+++ b/.changeset/guard-process-group-pgids.md
@@ -0,0 +1,5 @@
+---
+"@aliou/pi-processes": patch
+---
+
+Guard process-group helpers against non-positive pgids. `isProcessGroupAlive` now returns `false` and `killProcessGroup` now throws a `RangeError` when given a `0` or negative process-group ID, instead of probing or signaling the caller's own process group.
diff --git a/src/utils/process-group.test.ts b/src/utils/process-group.test.ts
new file mode 100644
index 0000000..a090941
--- /dev/null
+++ b/src/utils/process-group.test.ts
@@ -0,0 +1,20 @@
+import { describe, expect, it } from "vitest";
+import { isProcessGroupAlive, killProcessGroup } from "./process-group";
+
+describe("process-group helpers with non-positive pgids", () => {
+  it("isProcessGroupAlive(0) returns false", () => {
+    expect(isProcessGroupAlive(0)).toBe(false);
+  });
+
+  it("isProcessGroupAlive(-1) returns false", () => {
+    expect(isProcessGroupAlive(-1)).toBe(false);
+  });
+
+  it("killProcessGroup(0, ...) throws RangeError", () => {
+    expect(() => killProcessGroup(0, "SIGTERM")).toThrow(RangeError);
+  });
+
+  it("killProcessGroup(-1, ...) throws RangeError", () => {
+    expect(() => killProcessGroup(-1, "SIGTERM")).toThrow(RangeError);
+  });
+});
diff --git a/src/utils/process-group.ts b/src/utils/process-group.ts
index 728c65c..8decb49 100644
--- a/src/utils/process-group.ts
+++ b/src/utils/process-group.ts
@@ -3,6 +3,7 @@
  * Uses signal 0 to test existence without actually sending a signal.
  */
 export function isProcessGroupAlive(pgid: number): boolean {
+  if (!Number.isInteger(pgid) || pgid <= 0) return false;
   try {
     process.kill(-pgid, 0);
     return true;
@@ -18,5 +19,8 @@ export function isProcessGroupAlive(pgid: number): boolean {
  * Negative PID targets the process group.
  */
 export function killProcessGroup(pgid: number, signal: NodeJS.Signals): void {
+  if (!Number.isInteger(pgid) || pgid <= 0) {
+    throw new RangeError("Process group ID must be a positive integer");
+  }
   process.kill(-pgid, signal);
 }