diff --git a/src/main/java/org/jruby/prism/builder/IRBuilderPrism.java b/src/main/java/org/jruby/prism/builder/IRBuilderPrism.java
index 8adeb2f..d30a92f 100644
--- a/src/main/java/org/jruby/prism/builder/IRBuilderPrism.java
+++ b/src/main/java/org/jruby/prism/builder/IRBuilderPrism.java
@@ -2532,6 +2532,7 @@ protected void buildAssocs(Label testEnd, Operand original, Variable result, Has
                 // FIXME: only build literals (which are guaranteed to build without raising).
                 Operand key = build(assoc.key);
                 call(result, d, "key?", key);
+                copy(errorString, key); // Sets to symbol which will not be nil or a regular string.
                 cond_ne_true(testEnd, result);
 
                 String method = hasRest ? "delete" : "[]";