diff --git a/src/main.cpp b/src/main.cpp
index dccc1727..f129fb65 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1775,7 +1775,7 @@ bool static AlreadyHave(CTxDB& txdb, const CInv& inv)
 // The message start string is designed to be unlikely to occur in normal data.
 // The characters are rarely used upper ascii, not valid as UTF-8, and produce
 // a large 4-byte int at any alignment.
-char pchMessageStart[4] = { 0xf9, 0xbe, 0xb4, 0xd9 };
+unsigned char pchMessageStart[4] = { 0xf9, 0xbe, 0xb4, 0xd9 };
 
 
 bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
diff --git a/src/net.h b/src/net.h
index d896defc..056077fc 100644
--- a/src/net.h
+++ b/src/net.h
@@ -67,7 +67,7 @@ bool StopNode();
 //  (4) size
 //  (4) checksum
 
-extern char pchMessageStart[4];
+extern unsigned char pchMessageStart[4];
 
 class CMessageHeader
 {