diff --git a/src/emu/mux.c b/src/emu/mux.c
index b37b1b4..bd18502 100644
--- a/src/emu/mux.c
+++ b/src/emu/mux.c
@@ -142,6 +142,18 @@ mux_init(struct mux *mux,
 		return -1;
 	}
 
+	/* Ensure both channels are registered */
+	if (bay_find(bay, select->name) == NULL) {
+		err("mux_init: select channel %s not registered in bay\n",
+				select->name);
+		return -1;
+	}
+	if (bay_find(bay, output->name) == NULL) {
+		err("mux_init: output channel %s not registered in bay\n",
+				output->name);
+		return -1;
+	}
+
 	/* The output channel must accept multiple writes in the same
 	 * propagation phase while the channel is dirty, as we may write to the
 	 * input and select channel at the same time. */
diff --git a/test/unit/mux.c b/test/unit/mux.c
index 112fffd..504e09c 100644
--- a/test/unit/mux.c
+++ b/test/unit/mux.c
@@ -223,14 +223,24 @@ main(void)
 	}
 
 	/* Register all channels in the bay */
-	bay_register(&bay, &output);
-	bay_register(&bay, &select);
+	if (bay_register(&bay, &select) != 0)
+		die("bay_register failed\n");
+
 	for (int i = 0; i < N; i++) {
-		bay_register(&bay, &inputs[i]);
+		if(bay_register(&bay, &inputs[i]) != 0)
+			die("bay_register failed\n");
 	}
 
 	struct mux mux;
-	mux_init(&mux, &bay, &select, &output, NULL);
+	/* Attempt to init the mux without registering the output */
+	if (mux_init(&mux, &bay, &select, &output, NULL) == 0)
+		die("mux_init didn't fail\n");
+
+	if (bay_register(&bay, &output) != 0)
+		die("bay_register failed\n");
+
+	if (mux_init(&mux, &bay, &select, &output, NULL) != 0)
+		die("mux_init failed\n");
 
 	for (int i = 0; i < N; i++)
 		mux_add_input(&mux, value_int64(i), &inputs[i]);