diff --git a/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionScriptEngine.java b/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionScriptEngine.java
index 7870421817466..7d80a0d401013 100644
--- a/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionScriptEngine.java
+++ b/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionScriptEngine.java
@@ -371,7 +371,6 @@ private static ScoreScript.LeafFactory newScoreScript(Expression expr, SearchLoo
         // NOTE: if we need to do anything complicated with bindings in the future, we can just extend Bindings,
         // instead of complicating SimpleBindings (which should stay simple)
         SimpleBindings bindings = new SimpleBindings();
-        ReplaceableConstDoubleValueSource specialValue = null;
         boolean needsScores = false;
         for (String variable : expr.variables) {
             try {
@@ -379,8 +378,7 @@ private static ScoreScript.LeafFactory newScoreScript(Expression expr, SearchLoo
                     bindings.add("_score", DoubleValuesSource.SCORES);
                     needsScores = true;
                 } else if (variable.equals("_value")) {
-                    specialValue = new ReplaceableConstDoubleValueSource();
-                    bindings.add("_value", specialValue);
+                    bindings.add("_value", DoubleValuesSource.constant(0));
                     // noop: _value is special for aggregations, and is handled in ExpressionScriptBindings
                     // TODO: if some uses it in a scoring expression, they will get a nasty failure when evaluating...need a
                     // way to know this is for aggregations and so _value is ok to have...
diff --git a/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ReplaceableConstDoubleValueSource.java b/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ReplaceableConstDoubleValueSource.java
index 903ddaf72340e..697eca6226e3c 100644
--- a/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ReplaceableConstDoubleValueSource.java
+++ b/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ReplaceableConstDoubleValueSource.java
@@ -38,13 +38,8 @@ public boolean needsScores() {
     }
 
     @Override
-    public Explanation explain(LeafReaderContext ctx, int docId, Explanation scoreExplanation) throws IOException {
-        // TODO where is this explain called? I bet it's never tested, and probably never called.
-        ReplaceableConstDoubleValues fv = specialValues.get(ctx);
-        if (fv.advanceExact(docId)) {
-            return Explanation.match((float) fv.doubleValue(), "ReplaceableConstDoubleValues");
-        }
-        return Explanation.noMatch("ReplaceableConstDoubleValues");
+    public Explanation explain(LeafReaderContext ctx, int docId, Explanation scoreExplanation) {
+        throw new UnsupportedOperationException("explain is not supported for _value and should never be called");
     }
 
     @Override