diff --git a/constants/gba_constants.inc b/constants/gba_constants.inc
index 3ff857ee8..9f51b0f02 100644
--- a/constants/gba_constants.inc
+++ b/constants/gba_constants.inc
@@ -1,3 +1,6 @@
+#ifndef GUARD_CONSTANTS_GBA_CONSTANTS_INC
+#define GUARD_CONSTANTS_GBA_CONSTANTS_INC
+
 	.set PSR_USR_MODE,  0x00000010
 	.set PSR_FIQ_MODE,  0x00000011
 	.set PSR_IRQ_MODE,  0x00000012
@@ -511,3 +514,5 @@
 	.set BLDCNT_TGT2_OBJ,       1 << 12
 	.set BLDCNT_TGT2_BD,        1 << 13
 	.set BLDCNT_TGT2_ALL,       BLDCNT_TGT2_BG0 | BLDCNT_TGT2_BG1 | BLDCNT_TGT2_BG2 | BLDCNT_TGT2_BG3 | BLDCNT_TGT2_OBJ | BLDCNT_TGT2_BD
+
+#endif @ GUARD_CONSTANTS_GBA_CONSTANTS_INC
diff --git a/constants/global.inc b/constants/global.inc
index 621ba2af8..b9462fa26 100644
--- a/constants/global.inc
+++ b/constants/global.inc
@@ -1,3 +1,6 @@
+#ifndef GUARD_CONSTANTS_GLOBAL_INC
+#define GUARD_CONSTANTS_GLOBAL_INC
+
 	.set TRUE, 1
 	.set FALSE, 0
 
@@ -20,3 +23,5 @@
 
 	.set OBJ_IMAGE_ANIM_H_FLIP, 1 << 6
 	.set OBJ_IMAGE_ANIM_V_FLIP, 1 << 7
+
+#endif @ GUARD_CONSTANTS_GLOBAL_INC
diff --git a/constants/m4a_constants.inc b/constants/m4a_constants.inc
index 1a744dc7f..2599b6c4a 100644
--- a/constants/m4a_constants.inc
+++ b/constants/m4a_constants.inc
@@ -1,3 +1,6 @@
+#ifndef GUARD_CONSTANTS_M4A_CONSTANTS_INC
+#define GUARD_CONSTANTS_M4A_CONSTANTS_INC
+
 	.equiv ID_NUMBER, 0x68736d53
 
 	.equiv PCM_DMA_BUF_SIZE, 1584
@@ -250,3 +253,5 @@
 	struct_field o_CgbChannel_nextChannelPointer, 4
 	struct_field o_CgbChannel_dummy4, 8
 	struct_field CgbChannel_size, 0
+
+#endif  @ GUARD_CONSTANTS_M4A_CONSTANTS_INC
diff --git a/constants/tms_hms.inc b/constants/tms_hms.inc
index 3450aa73b..4ce6d9032 100644
--- a/constants/tms_hms.inc
+++ b/constants/tms_hms.inc
@@ -1,3 +1,6 @@
+#ifndef GUARD_CONSTANTS_TMS_HMS_INC
+#define GUARD_CONSTANTS_TMS_HMS_INC
+
 #include "constants/tms_hms.h"
 
 /* Expands to:
@@ -15,3 +18,5 @@ FOREACH_TM(EQUIV_TM)
 FOREACH_HM(EQUIV_HM)
 #undef EQUIV_TM
 #undef EQUIV_HM
+
+#endif @ GUARD_CONSTANTS_TMS_HMS_INC