diff --git a/src/bignum.h b/src/bignum.h
index cea8e1e35..0d57dc8a8 100644
--- a/src/bignum.h
+++ b/src/bignum.h
@@ -78,7 +78,8 @@ public:
         BN_clear_free(this);
     }
 
-    CBigNum(char n)             { BN_init(this); if (n >= 0) setulong(n); else setint64(n); }
+    //CBigNum(char n) is not portable.  Use 'signed char' or 'unsigned char'.
+    CBigNum(signed char n)      { BN_init(this); if (n >= 0) setulong(n); else setint64(n); }
     CBigNum(short n)            { BN_init(this); if (n >= 0) setulong(n); else setint64(n); }
     CBigNum(int n)              { BN_init(this); if (n >= 0) setulong(n); else setint64(n); }
     CBigNum(long n)             { BN_init(this); if (n >= 0) setulong(n); else setint64(n); }
@@ -296,7 +297,7 @@ public:
             psz++;
 
         // hex string to bignum
-        static char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
+        static signed char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
         *this = 0;
         while (isxdigit(*psz))
         {
diff --git a/src/script.h b/src/script.h
index 524d08b3e..1aac324f6 100644
--- a/src/script.h
+++ b/src/script.h
@@ -268,7 +268,8 @@ public:
     }
 
 
-    explicit CScript(char b)           { operator<<(b); }
+    //explicit CScript(char b) is not portable.  Use 'signed char' or 'unsigned char'.
+    explicit CScript(signed char b)    { operator<<(b); }
     explicit CScript(short b)          { operator<<(b); }
     explicit CScript(int b)            { operator<<(b); }
     explicit CScript(long b)           { operator<<(b); }
@@ -285,7 +286,8 @@ public:
     explicit CScript(const std::vector<unsigned char>& b) { operator<<(b); }
 
 
-    CScript& operator<<(char b)           { return push_int64(b); }
+    //CScript& operator<<(char b) is not portable.  Use 'signed char' or 'unsigned char'.
+    CScript& operator<<(signed char b)    { return push_int64(b); }
     CScript& operator<<(short b)          { return push_int64(b); }
     CScript& operator<<(int b)            { return push_int64(b); }
     CScript& operator<<(long b)           { return push_int64(b); }
diff --git a/src/uint256.h b/src/uint256.h
index bf3c55bcc..104b84970 100644
--- a/src/uint256.h
+++ b/src/uint256.h
@@ -305,7 +305,7 @@ public:
             psz += 2;
 
         // hex string to uint
-        static char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
+        static unsigned char phexdigit[256] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,1,2,3,4,5,6,7,8,9,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0xa,0xb,0xc,0xd,0xe,0xf,0,0,0,0,0,0,0,0,0 };
         const char* pbegin = psz;
         while (phexdigit[(unsigned char)*psz] || *psz == '0')
             psz++;
diff --git a/src/util.cpp b/src/util.cpp
index 19e48d3bd..9f2de3449 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -425,7 +425,7 @@ bool ParseMoney(const char* pszIn, int64& nRet)
 }
 
 
-static char phexdigit[256] =
+static signed char phexdigit[256] =
 { -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
   -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
   -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
@@ -461,12 +461,12 @@ vector<unsigned char> ParseHex(const char* psz)
     {
         while (isspace(*psz))
             psz++;
-        char c = phexdigit[(unsigned char)*psz++];
-        if (c == (char)-1)
+        signed char c = phexdigit[(unsigned char)*psz++];
+        if (c == (signed char)-1)
             break;
         unsigned char n = (c << 4);
         c = phexdigit[(unsigned char)*psz++];
-        if (c == (char)-1)
+        if (c == (signed char)-1)
             break;
         n |= c;
         vch.push_back(n);