diff --git a/src/main.cpp b/src/main.cpp
index 0e0fd28c4..a357079ba 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1860,7 +1860,7 @@ bool CheckDiskSpace(uint64 nAdditionalBytes)
 
 FILE* OpenBlockFile(unsigned int nFile, unsigned int nBlockPos, const char* pszMode)
 {
-    if (nFile == -1)
+    if ((nFile < 1) || (nFile == (unsigned int) -1))
         return NULL;
     FILE* file = fopen((GetDataDir() / strprintf("blk%04d.dat", nFile)).string().c_str(), pszMode);
     if (!file)
diff --git a/src/main.h b/src/main.h
index c48b57b93..965100d6d 100644
--- a/src/main.h
+++ b/src/main.h
@@ -138,8 +138,8 @@ public:
     }
 
     IMPLEMENT_SERIALIZE( READWRITE(FLATDATA(*this)); )
-    void SetNull() { nFile = -1; nBlockPos = 0; nTxPos = 0; }
-    bool IsNull() const { return (nFile == -1); }
+    void SetNull() { nFile = (unsigned int) -1; nBlockPos = 0; nTxPos = 0; }
+    bool IsNull() const { return (nFile == (unsigned int) -1); }
 
     friend bool operator==(const CDiskTxPos& a, const CDiskTxPos& b)
     {
@@ -178,8 +178,8 @@ public:
 
     CInPoint() { SetNull(); }
     CInPoint(CTransaction* ptxIn, unsigned int nIn) { ptx = ptxIn; n = nIn; }
-    void SetNull() { ptx = NULL; n = -1; }
-    bool IsNull() const { return (ptx == NULL && n == -1); }
+    void SetNull() { ptx = NULL; n = (unsigned int) -1; }
+    bool IsNull() const { return (ptx == NULL && n == (unsigned int) -1); }
 };
 
 
@@ -194,8 +194,8 @@ public:
     COutPoint() { SetNull(); }
     COutPoint(uint256 hashIn, unsigned int nIn) { hash = hashIn; n = nIn; }
     IMPLEMENT_SERIALIZE( READWRITE(FLATDATA(*this)); )
-    void SetNull() { hash = 0; n = -1; }
-    bool IsNull() const { return (hash == 0 && n == -1); }
+    void SetNull() { hash = 0; n = (unsigned int) -1; }
+    bool IsNull() const { return (hash == 0 && n == (unsigned int) -1); }
 
     friend bool operator<(const COutPoint& a, const COutPoint& b)
     {
diff --git a/src/net.cpp b/src/net.cpp
index 92b4a3173..745b51252 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -621,7 +621,7 @@ void ThreadSocketHandler2(void* parg)
         if (nSelect == SOCKET_ERROR)
         {
             int nErr = WSAGetLastError();
-            if (hSocketMax > -1)
+            if (hSocketMax > (SOCKET) -1)
             {
                 printf("socket select error %d\n", nErr);
                 for (unsigned int i = 0; i <= hSocketMax; i++)
diff --git a/src/script.cpp b/src/script.cpp
index 65e9b7c9a..0b103a80b 100644
--- a/src/script.cpp
+++ b/src/script.cpp
@@ -940,7 +940,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, co
                     // ([sig ...] num_of_signatures [pubkey ...] num_of_pubkeys -- bool)
 
                     int i = 1;
-                    if (stack.size() < i)
+                    if ((int)stack.size() < i)
                         return false;
 
                     int nKeysCount = CastToBigNum(stacktop(-i)).getint();
@@ -951,7 +951,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, co
                         return false;
                     int ikey = ++i;
                     i += nKeysCount;
-                    if (stack.size() < i)
+                    if ((int)stack.size() < i)
                         return false;
 
                     int nSigsCount = CastToBigNum(stacktop(-i)).getint();
@@ -959,7 +959,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, co
                         return false;
                     int isig = ++i;
                     i += nSigsCount;
-                    if (stack.size() < i)
+                    if ((int)stack.size() < i)
                         return false;
 
                     // Subset of script starting at the most recent codeseparator