diff --git a/src/compose/utils.ts b/src/compose/utils.ts
index 31796dd3..c870d363 100644
--- a/src/compose/utils.ts
+++ b/src/compose/utils.ts
@@ -494,7 +494,5 @@ export function normalizeLabels(labels: {
 		labels,
 		(_v, k) => !(_.startsWith(k, 'io.balena.') || _.startsWith(k, 'io.resin.')),
 	);
-	return _.assign({}, otherLabels, legacyLabels, balenaLabels) as {
-		[key: string]: string;
-	};
+	return _.assign({}, otherLabels, legacyLabels, balenaLabels);
 }
diff --git a/src/config/backend.ts b/src/config/backend.ts
index fa1a0b1e..a59577a2 100644
--- a/src/config/backend.ts
+++ b/src/config/backend.ts
@@ -130,7 +130,13 @@ export class RPiConfigBackend extends DeviceConfigBackend {
 						if (conf[key] == null) {
 							conf[key] = [];
 						}
-						(conf[key] as string[]).push(value);
+						const confArr = conf[key];
+						if (!_.isArray(confArr)) {
+							throw new Error(
+								`Expected '${key}' to have a config array but got ${typeof confArr}`,
+							);
+						}
+						confArr.push(value);
 					}
 					continue;
 				}