diff --git a/src/pika_config_valid.h b/src/pika_config_valid.h
index d3e520884..b13c95cc5 100644
--- a/src/pika_config_valid.h
+++ b/src/pika_config_valid.h
@@ -60,10 +60,14 @@
             #define PIKA_OPTIMIZE PIKA_OPTIMIZE_SIZE
         #endif
 
-        /* default syntax support level */
         #ifndef PIKA_SYNTAX_LEVEL
             #define PIKA_SYNTAX_LEVEL PIKA_SYNTAX_LEVEL_MINIMAL
         #endif
+
+        #ifndef PIKA_INIT_STRING_ENABLE
+            #define PIKA_INIT_STRING_ENABLE 0
+        #endif
+
     #endif
 
     /* default optimize */