diff --git a/src/battle_palace.c b/src/battle_palace.c
index d435f7e155..4033712b62 100644
--- a/src/battle_palace.c
+++ b/src/battle_palace.c
@@ -6,6 +6,7 @@
 #include "battle_tower.h"
 #include "frontier_util.h"
 #include "item.h"
+#include "string_util.h"
 #include "constants/items.h"
 
 // This file's functions.
diff --git a/src/battle_pyramid.c b/src/battle_pyramid.c
index 878ea4e706..01f1389252 100644
--- a/src/battle_pyramid.c
+++ b/src/battle_pyramid.c
@@ -15,6 +15,7 @@
 #include "sound.h"
 #include "task.h"
 #include "start_menu.h"
+#include "string_util.h"
 #include "trainer_see.h"
 #include "main.h"
 #include "load_save.h"
diff --git a/src/easy_chat.c b/src/easy_chat.c
index 7d25d1430b..e4233fb7f6 100644
--- a/src/easy_chat.c
+++ b/src/easy_chat.c
@@ -13,6 +13,7 @@
 #include "palette.h"
 #include "event_data.h"
 #include "easy_chat.h"
+#include "string_util.h"
 
 // Static type declarations
 
diff --git a/src/fldeff_strength.c b/src/fldeff_strength.c
index c9b91f97fe..f796ecea64 100644
--- a/src/fldeff_strength.c
+++ b/src/fldeff_strength.c
@@ -5,6 +5,7 @@
 #include "party_menu.h"
 #include "rom6.h"
 #include "script.h"
+#include "string_util.h"
 #include "task.h"
 #include "constants/event_objects.h"
 #include "constants/field_effects.h"