diff --git a/commands/gsd/set-profile.md b/commands/gsd/set-profile.md
index 70a01a093..66f560105 100644
--- a/commands/gsd/set-profile.md
+++ b/commands/gsd/set-profile.md
@@ -9,4 +9,4 @@ allowed-tools:
 
 Show the following output to the user verbatim, with no extra commentary:
 
-!`gsd-sdk query config-set-model-profile $ARGUMENTS --raw`
+!`if ! command -v gsd-sdk >/dev/null 2>&1; then printf '⚠ gsd-sdk not found in PATH — /gsd:set-profile requires it.\n\nInstall the GSD SDK:\n  npm install -g @gsd-build/sdk\n\nOr update GSD to get the latest packages:\n  /gsd-update\n'; exit 1; fi; gsd-sdk query config-set-model-profile $ARGUMENTS --raw`
diff --git a/tests/bug-2439-set-profile-gsd-sdk-preflight.test.cjs b/tests/bug-2439-set-profile-gsd-sdk-preflight.test.cjs
new file mode 100644
index 000000000..9df63d018
--- /dev/null
+++ b/tests/bug-2439-set-profile-gsd-sdk-preflight.test.cjs
@@ -0,0 +1,54 @@
+/**
+ * Regression test for bug #2439
+ *
+ * /gsd:set-profile crashed with `command not found: gsd-sdk` when the
+ * gsd-sdk binary was not installed or not in PATH. The command body
+ * invoked `gsd-sdk query config-set-model-profile` directly with no
+ * pre-flight check, so missing gsd-sdk produced an opaque shell error.
+ *
+ * Fix mirrors bug #2334: guard the invocation with `command -v gsd-sdk`
+ * and emit an install hint when absent.
+ */
+
+'use strict';
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+
+const COMMAND_PATH = path.join(__dirname, '..', 'commands', 'gsd', 'set-profile.md');
+
+describe('bug #2439: /gsd:set-profile gsd-sdk pre-flight check', () => {
+  const content = fs.readFileSync(COMMAND_PATH, 'utf-8');
+
+  test('command file exists', () => {
+    assert.ok(fs.existsSync(COMMAND_PATH), 'commands/gsd/set-profile.md should exist');
+  });
+
+  test('guards gsd-sdk invocation with command -v check', () => {
+    const sdkCall = content.indexOf('gsd-sdk query config-set-model-profile');
+    assert.ok(sdkCall !== -1, 'gsd-sdk query config-set-model-profile must be present');
+
+    const preamble = content.slice(0, sdkCall);
+    assert.ok(
+      preamble.includes('command -v gsd-sdk') || preamble.includes('which gsd-sdk'),
+      'set-profile must check for gsd-sdk in PATH before invoking it. ' +
+      'Without this guard the command crashes with exit 127 when gsd-sdk ' +
+      'is not installed (root cause of #2439).'
+    );
+  });
+
+  test('pre-flight error message references install/update path', () => {
+    const sdkCall = content.indexOf('gsd-sdk query config-set-model-profile');
+    const preamble = content.slice(0, sdkCall);
+    const hasInstallHint =
+      preamble.includes('@gsd-build/sdk') ||
+      preamble.includes('gsd-update') ||
+      preamble.includes('/gsd-update');
+    assert.ok(
+      hasInstallHint,
+      'Pre-flight error must point users at `npm install -g @gsd-build/sdk` or `/gsd-update`.'
+    );
+  });
+});