diff --git a/commands/boot.c b/commands/boot.c
index 8b3b407..102ca07 100644
--- a/commands/boot.c
+++ b/commands/boot.c
@@ -53,6 +53,8 @@
 		case 'w':
 			boot_set_watchdog_timeout(simple_strtoul(optarg, NULL, 0));
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/bootm.c b/commands/bootm.c
index 61b9086..c7cbdbe 100644
--- a/commands/bootm.c
+++ b/commands/bootm.c
@@ -97,7 +97,7 @@
 			data.dryrun = 1;
 			break;
 		default:
-			break;
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/dhcp.c b/commands/dhcp.c
index eb98bfc..4f4f549 100644
--- a/commands/dhcp.c
+++ b/commands/dhcp.c
@@ -45,6 +45,8 @@
 		case 'r':
 			retries = simple_strtoul(optarg, NULL, 10);
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/fbtest.c b/commands/fbtest.c
index d070d1f..bd0e140 100644
--- a/commands/fbtest.c
+++ b/commands/fbtest.c
@@ -137,6 +137,8 @@
 		case 'c':
 			color = simple_strtoul(optarg, NULL, 16);
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/hashsum.c b/commands/hashsum.c
index d05e571..70aab2c 100644
--- a/commands/hashsum.c
+++ b/commands/hashsum.c
@@ -42,6 +42,8 @@
 			key = optarg;
 			keylen = strlen(key);
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/help.c b/commands/help.c
index 3d36d9b..819c406 100644
--- a/commands/help.c
+++ b/commands/help.c
@@ -98,6 +98,8 @@
 		case 'a':
 			all = 1;
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/hwclock.c b/commands/hwclock.c
index 6a0fe03..5073618 100644
--- a/commands/hwclock.c
+++ b/commands/hwclock.c
@@ -123,6 +123,8 @@
 			ntp_to_hw = 1;
 			ntpserver = optarg;
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/linux16.c b/commands/linux16.c
index bb678bd..db8d081 100644
--- a/commands/linux16.c
+++ b/commands/linux16.c
@@ -176,6 +176,8 @@
 				}
 			}
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/loadb.c b/commands/loadb.c
index 6180ce3..8c3906c 100644
--- a/commands/loadb.c
+++ b/commands/loadb.c
@@ -634,8 +634,7 @@
 			console_dev_name = optarg;
 			break;
 		default:
-			perror(argv[0]);
-			return 1;
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/loadxy.c b/commands/loadxy.c
index a4b1bec..a2aab0f 100644
--- a/commands/loadxy.c
+++ b/commands/loadxy.c
@@ -67,8 +67,7 @@
 			cname = optarg;
 			break;
 		default:
-			perror(argv[0]);
-			return 1;
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/ls.c b/commands/ls.c
index ce02f16..331a4d2 100644
--- a/commands/ls.c
+++ b/commands/ls.c
@@ -143,6 +143,8 @@
 		case 'l':
 			flags &= ~LS_COLUMN;
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/mem.c b/commands/mem.c
index 907f1f7..29eaa80 100644
--- a/commands/mem.c
+++ b/commands/mem.c
@@ -74,7 +74,7 @@
 			*swab = 1;
 			break;
 		default:
-			return -1;
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/menutree.c b/commands/menutree.c
index ea5f65f..cf37b01 100644
--- a/commands/menutree.c
+++ b/commands/menutree.c
@@ -26,6 +26,8 @@
 		case 'm':
 			path = optarg;
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/reset.c b/commands/reset.c
index 8300480..6eac532 100644
--- a/commands/reset.c
+++ b/commands/reset.c
@@ -34,6 +34,8 @@
 		case 'f':
 			shutdown_flag = 0;
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/splash.c b/commands/splash.c
index 15b296b..2b70b29 100644
--- a/commands/splash.c
+++ b/commands/splash.c
@@ -41,6 +41,8 @@
 		case 'y':
 			s.y = simple_strtoul(optarg, NULL, 0);
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/usb.c b/commands/usb.c
index 48c6619..9a23aa2 100644
--- a/commands/usb.c
+++ b/commands/usb.c
@@ -123,6 +123,8 @@
 		case 's':
 			show = 1;
 			break;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}
 
diff --git a/commands/usbserial.c b/commands/usbserial.c
index e80b315..ad6bc63 100644
--- a/commands/usbserial.c
+++ b/commands/usbserial.c
@@ -44,6 +44,8 @@
 		case 'd':
 			usb_serial_unregister();
 			return 0;
+		default:
+			return COMMAND_ERROR_USAGE;
 		}
 	}