diff --git a/src/json.hpp b/src/json.hpp
index 79df1f78..d1338969 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -5757,10 +5757,9 @@ class basic_json
                 ++anchor;
                 ++array_index;
 
-                first = calculate_key();
-
                 if (array_index < container_size)
                 {
+                    first = calculate_key();
                     second = *anchor;
                 }
 
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index 585aa205..f8547367 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -5757,10 +5757,9 @@ class basic_json
                 ++anchor;
                 ++array_index;
 
-                first = calculate_key();
-
                 if (array_index < container_size)
                 {
+                    first = calculate_key();
                     second = *anchor;
                 }