diff --git a/packages/client/test/helpers/ensureBuilt.ts b/packages/client/test/helpers/ensureBuilt.ts
index 4611a367c9..5ba15cef5d 100644
--- a/packages/client/test/helpers/ensureBuilt.ts
+++ b/packages/client/test/helpers/ensureBuilt.ts
@@ -93,7 +93,9 @@ export async function ensureBuilt(pkgDir: string): Promise<void> {
         try {
             if (!haveAll()) {
                 try {
+                    // pnpm is a pnpm.cmd shim on Windows, which execFile can only start through a shell.
                     await execFileAsync('pnpm', ['build'], {
+                        shell: process.platform === 'win32',
                         cwd: pkgDir,
                         timeout: BUILD_TIMEOUT_MS,
                         maxBuffer: 16 * 1024 * 1024
diff --git a/packages/server/test/helpers/ensureBuilt.ts b/packages/server/test/helpers/ensureBuilt.ts
index e51ce463f9..ff7546bd51 100644
--- a/packages/server/test/helpers/ensureBuilt.ts
+++ b/packages/server/test/helpers/ensureBuilt.ts
@@ -87,7 +87,9 @@ export async function ensureBuilt(pkgDir: string): Promise<void> {
         try {
             if (!haveAll()) {
                 try {
+                    // pnpm is a pnpm.cmd shim on Windows, which execFile can only start through a shell.
                     await execFileAsync('pnpm', ['build'], {
+                        shell: process.platform === 'win32',
                         cwd: pkgDir,
                         timeout: BUILD_TIMEOUT_MS,
                         maxBuffer: 16 * 1024 * 1024