diff --git a/backend/util-common.ts b/backend/util-common.ts
index c7eabec..ddbcc65 100644
--- a/backend/util-common.ts
+++ b/backend/util-common.ts
@@ -385,7 +385,11 @@ function traverseYAML(pair : Pair, env : DotenvParseOutput) : void {
             if (item instanceof Pair) {
                 traverseYAML(item, env);
             } else if (item instanceof Scalar) {
-                item.value = envsubst(item.value, env);
+                let value = item.value as unknown;
+
+                if (typeof(value) === "string") {
+                    item.value = envsubst(value, env);
+                }
             }
         }
     // @ts-ignore