2 files changed, 6 insertions, 1 deletions
diff --git a/src/mongo/db/update/update_driver.cpp b/src/mongo/db/update/update_driver.cpp
index 7caaa4ab8a6..7ae41480779 100644
--- a/src/mongo/db/update/update_driver.cpp
+++ b/src/mongo/db/update/update_driver.cpp
@@ -166,7 +166,7 @@ Status UpdateDriver::parse(
     clear();
 
     // Check if the update expression is a full object replacement.
-    if (*updateExpr.firstElementFieldName() != '$') {
+    if (isDocReplacement(updateExpr)) {
         if (multi) {
             return Status(ErrorCodes::FailedToParse, "multi update only works with $ operators");
         }
@@ -581,4 +581,8 @@ void UpdateDriver::clear() {
     _positional = false;
 }
 
+bool UpdateDriver::isDocReplacement(const BSONObj& updateExpr) {
+    return *updateExpr.firstElementFieldName() != '$';
+}
+
 }  // namespace mongo
diff --git a/src/mongo/db/update/update_driver.h b/src/mongo/db/update/update_driver.h
index 337a1abfe87..e551d5fa2e8 100644
--- a/src/mongo/db/update/update_driver.h
+++ b/src/mongo/db/update/update_driver.h
@@ -126,6 +126,7 @@ public:
     size_t numMods() const;
 
     bool isDocReplacement() const;
+    static bool isDocReplacement(const BSONObj& updateExpr);
 
     bool modsAffectIndices() const;
     void refreshIndexKeys(const UpdateIndexData* indexedFields);