diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Eval.java b/src/main/java/com/google/devtools/build/lib/syntax/Eval.java
index 6cb3133..e42fb64 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Eval.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Eval.java
@@ -607,10 +607,17 @@
             if (result != null) {
               return result;
             }
-            String error =
-                ValidationEnvironment.createInvalidIdentifierException(
-                    name, fr.thread.getVariableNames());
-            throw new EvalException(id.getStartLocation(), error);
+
+            // Assuming validation was successfully applied before execution
+            // (which is not yet true for copybara, but will be soon),
+            // then the identifier must have been resolved but the
+            // resolution was not annotated onto the syntax tree---because
+            // it's a BUILD file that may share trees with the prelude.
+            // So this error does not mean "undefined variable" (morally a
+            // static error), but "variable was (dynamically) referenced
+            // before being bound", as in 'print(x); x=1'.
+            throw new EvalException(
+                id.getStartLocation(), "variable '" + name + "' is referenced before assignment");
           }
 
           Object result;
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
index 11abce1..167be97 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
@@ -231,8 +231,7 @@
     }
   }
 
-  // This is exposed to Eval until validation becomes a precondition for evaluation.
-  static String createInvalidIdentifierException(String name, Set<String> candidates) {
+  private static String createInvalidIdentifierException(String name, Set<String> candidates) {
     if (name.equals("$error$")) {
       return "contains syntax error(s)";
     }
diff --git a/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java b/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java
index 240d39a..e53b709 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/EvaluationTest.java
@@ -466,11 +466,13 @@
   @Test
   public void testListComprehensionDefinitionOrder() throws Exception {
     new BuildTest()
-        .testIfErrorContains("name 'y' is not defined", "[x for x in (1, 2) if y for y in (3, 4)]");
+        .testIfErrorContains(
+            "variable 'y' is referenced before assignment", //
+            "[x for x in (1, 2) if y for y in (3, 4)]");
 
     new SkylarkTest()
         .testIfErrorContains(
-            "local variable 'y' is referenced before assignment",
+            "local variable 'y' is referenced before assignment", //
             "[x for x in (1, 2) if y for y in (3, 4)]");
   }