diff --git a/packages/sanddance-specs/src/expr.ts b/packages/sanddance-specs/src/expr.ts
index a9fc8707..6c9b090a 100644
--- a/packages/sanddance-specs/src/expr.ts
+++ b/packages/sanddance-specs/src/expr.ts
@@ -9,7 +9,11 @@
  * examples: "source.x", "target['x']", "[my.field]"
  */
 export function safeFieldName(field: string) {
-    return field.replace('.', '\\.').replace('[', '\\[').replace(']', '\\]');
+    return field
+        .replace(/\./g, '\\.')
+        .replace(/\[/g, '\\[')
+        .replace(/\]/g, '\\]')
+    ;
 }
 
 /**