diff --git a/topdown/eval.go b/topdown/eval.go
index c0f77faaea..432700bd4c 100644
--- a/topdown/eval.go
+++ b/topdown/eval.go
@@ -567,19 +567,24 @@ func (e *eval) evalNotPartialSupport(negationID uint64, expr *ast.Expr, unknowns
 	}
 
 	// Save expression that refers to support rule set.
-	expr = expr.Copy()
+
+	terms := expr.Terms
+	expr.Terms = nil // Prevent unnecessary copying the terms.
+	cpy := expr.Copy()
+	expr.Terms = terms
+
 	if len(args) > 0 {
 		terms := make([]*ast.Term, len(args)+1)
 		terms[0] = term
 		for i := 0; i < len(args); i++ {
 			terms[i+1] = args[i]
 		}
-		expr.Terms = terms
+		cpy.Terms = terms
 	} else {
-		expr.Terms = term
+		cpy.Terms = term
 	}
 
-	return e.saveInlinedNegatedExprs([]*ast.Expr{expr}, func() error {
+	return e.saveInlinedNegatedExprs([]*ast.Expr{cpy}, func() error {
 		return e.next(iter)
 	})
 }
diff --git a/topdown/input.go b/topdown/input.go
index a74ef199f6..b3d542e1af 100644
--- a/topdown/input.go
+++ b/topdown/input.go
@@ -16,10 +16,7 @@ var errBadPath = fmt.Errorf("bad document path")
 func mergeTermWithValues(exist *ast.Term, pairs [][2]*ast.Term) (*ast.Term, error) {
 
 	var result *ast.Term
-
-	if exist != nil {
-		result = exist.Copy()
-	}
+	var init bool
 
 	for _, pair := range pairs {
 
@@ -31,33 +28,45 @@ func mergeTermWithValues(exist *ast.Term, pairs [][2]*ast.Term) (*ast.Term, erro
 
 		if len(target) == 1 {
 			result = pair[1]
-		} else if result == nil {
-			result = ast.NewTerm(makeTree(target[1:], pair[1]))
+			init = true
 		} else {
-			node := result
-			done := false
-			for i := 1; i < len(target)-1 && !done; i++ {
-				if child := node.Get(target[i]); child == nil {
+			if !init {
+				result = exist.Copy()
+				init = true
+			}
+
+			if result == nil {
+				result = ast.NewTerm(makeTree(target[1:], pair[1]))
+			} else {
+				node := result
+				done := false
+				for i := 1; i < len(target)-1 && !done; i++ {
+					if child := node.Get(target[i]); child == nil {
+						obj, ok := node.Value.(ast.Object)
+						if !ok {
+							return nil, errConflictingDoc
+						}
+						obj.Insert(target[i], ast.NewTerm(makeTree(target[i+1:], pair[1])))
+						done = true
+					} else {
+						node = child
+					}
+				}
+				if !done {
 					obj, ok := node.Value.(ast.Object)
 					if !ok {
 						return nil, errConflictingDoc
 					}
-					obj.Insert(target[i], ast.NewTerm(makeTree(target[i+1:], pair[1])))
-					done = true
-				} else {
-					node = child
-				}
-			}
-			if !done {
-				obj, ok := node.Value.(ast.Object)
-				if !ok {
-					return nil, errConflictingDoc
+					obj.Insert(target[len(target)-1], pair[1])
 				}
-				obj.Insert(target[len(target)-1], pair[1])
 			}
 		}
 	}
 
+	if !init {
+		result = exist
+	}
+
 	return result, nil
 }