diff --git a/src/cli/commands/deploy/deploy.spec.ts b/src/cli/commands/deploy/deploy.spec.ts
index 313de36b..9d12fee5 100644
--- a/src/cli/commands/deploy/deploy.spec.ts
+++ b/src/cli/commands/deploy/deploy.spec.ts
@@ -307,5 +307,13 @@ describe("deploy", () => {
       expect(env.FUNCTION_LANGUAGE_VERSION).toBe(DEFAULT_VERSION.DotnetIsolated);
       expect(SUPPORTED_VERSIONS.DotnetIsolated).toContain(env.FUNCTION_LANGUAGE_VERSION);
     });
+
+    it("should print an error when --env is an empty string", async () => {
+      await deploy({
+        outputLocation: "/test-output",
+        env: "",
+      });
+      expect(logger.error).toHaveBeenNthCalledWith(1, "Invalid --env: cannot be empty. Use 'preview' or omit the flag.");
+    });
   });
 });
diff --git a/src/cli/commands/deploy/deploy.ts b/src/cli/commands/deploy/deploy.ts
index f748accd..969a7c77 100644
--- a/src/cli/commands/deploy/deploy.ts
+++ b/src/cli/commands/deploy/deploy.ts
@@ -255,6 +255,10 @@ export async function deploy(options: SWACLIConfig) {
   // set the DEPLOYMENT_ENVIRONMENT env variable only when the user has provided
   // a deployment environment which is not "production".
   if (options.env?.toLowerCase() !== "production" && options.env?.toLowerCase() !== "prod") {
+    if (options.env !== undefined && !options.env.trim()) {
+      logger.error("Invalid --env: cannot be empty. Use 'preview' or omit the flag.");
+      return;
+    }
     deployClientEnv.DEPLOYMENT_ENVIRONMENT = options.env;
   }