diff --git a/desmume/src/SPU.cpp b/desmume/src/SPU.cpp
index 3497eb819..398413a04 100644
--- a/desmume/src/SPU.cpp
+++ b/desmume/src/SPU.cpp
@@ -40,12 +40,12 @@ extern SoundInterface_struct *SNDCoreList[];
 #define CHANSTAT_STOPPED          0
 #define CHANSTAT_PLAY             1
 
-s8 indextbl[8] =
+const s8 indextbl[8] =
 {
 	-1, -1, -1, -1, 2, 4, 6, 8
 };
 
-u16 adpcmtbl[89] =
+const u16 adpcmtbl[89] =
 {
 	0x0007, 0x0008, 0x0009, 0x000A, 0x000B, 0x000C, 0x000D, 0x000E, 0x0010,
 	0x0011, 0x0013, 0x0015, 0x0017, 0x0019, 0x001C, 0x001F, 0x0022, 0x0025,
@@ -59,7 +59,7 @@ u16 adpcmtbl[89] =
 	0x41B2, 0x4844, 0x4F7E, 0x5771, 0x602F, 0x69CE, 0x7462, 0x7FFF
 };
 
-s16 wavedutytbl[8][8] = {
+const s16 wavedutytbl[8][8] = {
 	{ -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, 0x7FFF },
 	{ -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, 0x7FFF, 0x7FFF },
 	{ -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, -0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF },