diff --git a/sha1.cpp b/sha1.cpp
index 770f6f5..6df0d55 100755
--- a/sha1.cpp
+++ b/sha1.cpp
@@ -8,7 +8,7 @@
 #define SHA1_K40 0x8f1bbcdc
 #define SHA1_K60 0xca62c1d6
 
-uint8_t sha1InitState[] PROGMEM = {
+const uint8_t sha1InitState[] PROGMEM = {
   0x01,0x23,0x45,0x67, // H0
   0x89,0xab,0xcd,0xef, // H1
   0xfe,0xdc,0xba,0x98, // H2