diff --git a/core/Charstring.cc b/core/Charstring.cc
index 68ee676c265c36f7732aa45abd4597cd317d27c0..afb70a39f3adc141bd5e43803f33034e6db2c009 100644
--- a/core/Charstring.cc
+++ b/core/Charstring.cc
@@ -1322,7 +1322,7 @@ int CHARSTRING::XER_encode(const XERdescriptor_t& p_td,
 * Translates a Base64 value to either its 6-bit reconstruction value
 * or a negative number indicating some other meaning.
 * Public domain from http://iharder.net/base64 */
-char  base64_decoder_table[256] =
+signed char  base64_decoder_table[256] =
 {
   -9,-9,-9,-9,-9,-9,-9,-9,-9,                 // Decimal  0 -  8
   -5,-5,                                      // Whitespace: Tab and Linefeed
diff --git a/core/Universal_charstring.cc b/core/Universal_charstring.cc
index a9496f8bdf743070dfc4751a023d5ea029086811..be1369a7f1187e3014c30f2bed7ebcdbf0b2486a 100644
--- a/core/Universal_charstring.cc
+++ b/core/Universal_charstring.cc
@@ -2053,7 +2053,7 @@ inline
 static char
 in_word_set (const char *str, unsigned int len)
 {
-  static char wordlist[] =
+  static signed char wordlist[] =
     {
       -1, -1,
       12, // FF
diff --git a/xsdconvert/converter.cc b/xsdconvert/converter.cc
index 86153856e7307de45dad3406fe3eb2419c461523..45f54e25bc898d9d6653674c0bc449d226cd3d6c 100644
--- a/xsdconvert/converter.cc
+++ b/xsdconvert/converter.cc
@@ -72,7 +72,7 @@ int main(int argc, char **argv) {
 
   // The file holding a list of the XSD files.
   const char *from_file = NULL;
-  char c;
+  signed char c;
   opterr = 0;
 
   while ((c = getopt(argc, argv, "cdef:ghJ:mnopqstvwxz")) != -1) {