diff --git a/src/cli/commands/deploy/deploy.spec.ts b/src/cli/commands/deploy/deploy.spec.ts
index 313de36b..82a9025f 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 a named environment (e.g. 'preview') or omit the flag.");
+    });
   });
 });
diff --git a/src/cli/commands/deploy/deploy.ts b/src/cli/commands/deploy/deploy.ts
index f748accd..94b1ada3 100644
--- a/src/cli/commands/deploy/deploy.ts
+++ b/src/cli/commands/deploy/deploy.ts
@@ -60,6 +60,12 @@ export async function deploy(options: SWACLIConfig) {
     }
   }
 
+  // make sure --env is not an empty string
+  if (options.env !== undefined && !options.env.trim()) {
+    logger.error("Invalid --env: cannot be empty. Use a named environment (e.g. 'preview') or omit the flag.");
+    return;
+  }
+
   logger.silly(`Resolving outputLocation=${outputLocation} full path...`);
   let resolvedOutputLocation = path.resolve(appLocation, outputLocation as string);